A method of coating an underwater sound collecting microphone

Abstract

The present application relates to the field of metal material coating, more particularly to a coating method of underwater sound collecting microphone. The coating method of underwater sound collecting microphone mainly comprises: coating a specific shielding glue on the product, controlling the width and thickness of the shielding glue, then carrying out plasma cleaning, chemical vapor deposition of parylene film layer, and removing the shielding glue; the underwater sound collecting microphone after coating treatment has excellent waterproof performance, no corrosion and rust phenomenon occurs, and the sensitivity has no obvious change, the signal noise is less, the diaphragm is not damaged, and has good practical use effect.

Description

Technical Field

[0001] This invention relates to the field of metal material coating, and more specifically to a coating method for an underwater microphone. Background Technology

[0002] Underwater microphones are primarily used in specialized operations, including scientific research and diving. Due to the specific working conditions, underwater microphones often require encapsulation for protection. However, even with encapsulation, moisture can still penetrate the internal microphone array, potentially causing array failure. Furthermore, the pressure in underwater environments necessitates that the microphone's diaphragm possess a certain level of pressure resistance. Therefore, it is essential to protect the microphone array and reinforce the diaphragm without significantly affecting the device's sensitivity.

[0003] A common and effective method is vacuum chemical vapor deposition (CVD) to deposit a Parylene film layer, which meets the requirements well. Parylene, a derivative of parylene, has excellent penetrating power and can deposit a uniformly thick, transparent insulating coating on equipment components, providing a complete and high-quality protective coating for underwater microphones. This effectively resists the damage from acids, alkalis, salt spray, mold, and various corrosive gases. In addition to its excellent protective properties, the Parylene film layer also has good tensile and toughness mechanical properties, which minimizes the obstruction to the diaphragm's operation. It can also penetrate into the microphone cavity to form a uniformly thick and fully conformal film layer.

[0004] Underwater microphones are MEMS (Micro-Electro-Mechanical Systems) devices, which are generally miniaturized. Their pads are designed to be only 0.1-0.2 mm thick, making pre-coating masking extremely difficult. Only by selecting precision equipment, suitable masking materials, and appropriate implementation processes can it be achieved to meet the requirements of small size, high precision, and suitability for Piriton film layers.

[0005] The prior art CN110113892B discloses a multilayer composite protective layer and method for PCBs. The main processing steps include first performing surface treatment, then coating with nano-SiO2, and then sequentially coating with a pyrene film layer and an epoxy resin film layer. After the above process, the waterproof performance and mechanical properties of the PCB can be significantly improved. However, for underwater microphones, in addition to basic waterproof performance, it is also necessary to ensure the vibration performance of the microphone diaphragm. Therefore, it is necessary to strictly limit the type of adhesive and coating parameters. Summary of the Invention

[0006] To address the aforementioned technical problems, the present invention provides a coating method for an underwater microphone, comprising at least the following steps:

[0007] S1. Check whether the diaphragm of the underwater microphone is damaged and whether the surface is clean. Select an underwater microphone with an undamaged diaphragm and a clean surface.

[0008] S2. Place the underwater microphone onto the tooling fixture;

[0009] S3. Use a high-precision dispensing machine to apply masking adhesive to the areas that need to be masked.

[0010] S4. Place in a curing oven for drying, curing, and shaping;

[0011] S5. Remove the cured, shaped, and dried product from the tooling fixture and place it on the coating fixture.

[0012] S6. Perform plasma cleaning;

[0013] S7. Place the coating fixture onto the coating tooling and install it into the process chamber of the coating equipment.

[0014] S8. Start the coating program and use Piriton for chemical vapor deposition coating.

[0015] S9. When the coating thickness reaches 2-5μm, turn off the coating program;

[0016] S10. Remove the coating fixture, test the film thickness on the monitoring sheet. If the thickness is qualified, remove the product.

[0017] S11. Remove the masking adhesive;

[0018] S12. Inspect the appearance of the product. If the film layer is uniform and undamaged, it is considered qualified.

[0019] Preferably, the masking adhesive includes one of UV adhesive, sealant, solder resist adhesive, and pressure-sensitive adhesive.

[0020] Preferably, the UV adhesive is an acrylate urethane with a viscosity of 100,000-150,000 cps at 25°C, an elongation of 100-300%, and a tensile strength of 2-5.5 psi.

[0021] More preferably, the UV adhesive has a viscosity of 125,000 cps at 25°C, an elongation of 140%, and a tensile strength of 3.37 psi; as an implementable example, the UV adhesive model is [model number missing]. 9-20479-B-REV-A, purchased from DYMAX.

[0022] Preferably, the sealant includes ITW CHEMASK CM8 solder resist.

[0023] Preferably, the viscosity of the solder resist is 20,000-50,000 cps at 25°C, and the density is 0.8-1 g / cm³. 3 As an feasible example, the viscosity of the solder resist is 20,000-30,000 cps at 25°C, and the density is 0.9 g / cm³. 3 The model number is SM-120B, purchased from Shenzhen Guoran New Materials.

[0024] Preferably, the viscosity of the pressure-sensitive adhesive is 3000-7000 cps; as an implementable example, the viscosity of the pressure-sensitive adhesive is 5000 cps, and the model is BLJ-2232 adhesive.

[0025] More preferably, the masking adhesive is a UV adhesive.

[0026] Underwater microphones often require masking before applying paraffin coating. Therefore, choosing the right masking adhesive is crucial. The adhesive must not only have excellent peelability but also avoid containing corrosive halogens, as these can cause corrosion and rust on the microphone's circuitry. The inventors tested four commonly used metal circuit board adhesives: sealant, solder resist, pressure-sensitive adhesive, and UV adhesive. They found that using ITW CHEMASK CM8 solder resist caused corrosion to the underwater microphone components. This may be due to the fact that ITW CHEMASK... CM8 solder resist contains a small amount of halogens, which can corrode the surface of metal circuit boards. Furthermore, the sealant is prone to brittleness under large temperature variations, such as underwater, affecting its sealing performance. Additionally, the shear strength of the sealant layer is low, unable to withstand significant tensile stress, and it cannot remain stable under high underwater pressure. The film-forming materials in solder resist mainly include phenolic resin, epoxy resin, and alkyd resin, all of which require heating to 130℃~150℃ for curing. While these materials are inexpensive and have high bonding strength, they also have drawbacks such as high heating temperatures, long curing times, potential deformation of printed circuit boards, high energy consumption, and inability to achieve continuous production. Moreover, the rapid curing speed of solder resist makes it difficult to form a uniform adhesive layer on the surface of a water-washable microphone, and noticeable stringing occurs during the application process. Pressure-sensitive adhesives typically require curing at temperatures above 170℃, and the thermal stress from these temperatures can cause the diaphragm of the underwater microphone to rupture, significantly impacting sound reception. The inventors have discovered that DYMAX, a UV adhesive used as a masking adhesive, has a viscosity of 125,000 cps at 25°C, an elongation of 140%, a tensile strength of 3.37 psi, and is primarily composed of urethane acrylate. The UV adhesive 9-20479-B-REV-A can effectively prevent stringing and corrosion. In addition, the UV adhesive can be cured at room temperature after application without high temperature conditions. It is also easy to peel off after application without leaving any residue, which is conducive to the uniformity and integrity of the Piriton film layer.

[0027] Preferably, the masking adhesive has a coating width of 0.2-0.35 mm and a length of 2-3 mm.

[0028] Extending inward from the edge of the underwater microphone, the lower limit width is typically 0.23mm, and the upper limit is 0.33mm. If the coating thickness is less than the lower limit width, it means that the UV adhesive protection is ineffective, causing the pads to be covered by the Perylene film layer. Since the Perylene film layer is an insulating film, the electrical signal converted by the diaphragm cannot be effectively transmitted to the processing unit, thus significantly affecting the microphone's sound reception. If the masking adhesive thickness exceeds the upper limit width, it means that the UV adhesive protection is excessive, and the UV adhesive is applied to the diaphragm. The diaphragm is a silicon film of about 0.1μm, which can only deform within a small range and is very brittle. If the UV adhesive is applied, it needs to be removed after the Perylene film layer is deposited. The UV adhesive has a certain probability of damaging the diaphragm. In addition, if the coating width is too large, the diaphragm cannot be covered by the Perylene film layer, which can also lead to inconsistent film vibration or water vapor penetration, resulting in corrosion and rust.

[0029] Preferably, the plasma cleaning implementation of step S6 includes: using a radio frequency power supply to excite inert gas into plasma to clean the product in the coating fixture.

[0030] More preferably, the inert gas is argon.

[0031] Preferably, in step S8, after starting the coating process, a coupling agent is added and evaporated to deposit onto the product surface.

[0032] This invention does not further limit the coupling agent; any agent that can improve the adhesion between the phenelzine and the masking adhesive layer is acceptable, including but not limited to: one of KH-174, KH-550, KH-560, KH-570, and KH580; KH-570 is the preferred coupling agent in this invention.

[0033] Preferably, the paraffin includes one of type C paraffin, type N paraffin, type D paraffin, AF4 / HT paraffin, and AF4 / HT paraffin; in this invention, type C paraffin is preferred as the coating material. Type C paraffin has excellent physical and electrical properties, as well as low permeability in corrosive gas environments and humid and hot environments, and has a low cost, making it a preferred material for waterproofing, corrosion resistance, and salt spray resistance of underwater microphones.

[0034] The present invention uses a plasma cleaning process. The plasma has a physical impact on the product, which generates some active bonds. These active bonds are conducive to forming chemical bonds between the molecules of the phenelzine film. Then, KH-570 coupling agent liquid evaporation is used to form a nanoscale coupling agent layer on the surface of the product substrate, which further increases the adhesion between the C-type phenelzine film layer and the substrate.

[0035] Preferably, in step S8, the deposition rate of chemical vapor deposition is 0.1-1 μm / h, and the deposition pressure is 8-13 mTorr.

[0036] In this invention, the chemical vapor deposition rate of phenelzine is relatively low and the deposition pressure is moderate, which is conducive to improving uniformity and resulting in a higher density of the phenelzine film.

[0037] Preferably, the perylene chemical vapor deposition is not uniform throughout the entire process. During the first 1-2 hours of chemical vapor deposition, the deposition rate is 0.6 μm / h, during the next 0.5-1 hour, the deposition rate is 0.7 μm / h, and during the middle 3-4 hours, the deposition rate is 0.8 μm / h. This can further improve the density of the perylene film layer, thereby improving the protective performance of the underwater microphone.

[0038] Beneficial effects

[0039] (1) In this invention, UV adhesive is selected as the masking adhesive. It can be used normally after curing at room temperature. It does not contain corrosive halogens, so it will not corrode the components of the underwater radio, nor will it affect the sensitivity and sound reception of the microphone.

[0040] (2) In order to improve the masking performance of the masking adhesive, the present invention limits the thickness and width of the masking adhesive layer, which can improve the protective effect of the Piriton film layer on the underwater microphone.

[0041] (3) The present invention employs plasma cleaning and coupling agent liquid evaporation operations, which can further improve the bonding strength between the Piriton membrane layer and the substrate.

[0042] (4) In this invention, a smaller deposition rate is selected during the chemical vapor deposition of phenelzine to ensure a higher density of the phenelzine film.

[0043] (5) The underwater microphone treated by the coating method described in this invention has no significant change in sensitivity, less signal noise, and no damage to the diaphragm, and has a very good practical effect. Attached Figure Description

[0044] Figure 1 This is a partial view of the underwater microphone treated with the coating process in Comparative Example 2. Detailed Implementation

[0045] Example 1

[0046] This example provides a coating method for an underwater microphone, specifically the following steps:

[0047] S1. Check whether the diaphragm of the underwater microphone is damaged and whether the surface is clean. Select an underwater microphone with an undamaged diaphragm and a clean surface.

[0048] S2. Place the underwater microphone onto the tooling fixture;

[0049] S3. Using a high-precision dispensing machine, apply masking adhesive UV glue to the area that needs to be masked. The width of the adhesive coating is 0.2-0.3mm and the length is 3mm.

[0050] S4. Place in a UV curing oven for drying, curing, and shaping, with a curing wavelength of 400nm, a curing energy of 2000mJ, and a curing time of 10 seconds;

[0051] S5. Remove the cured, shaped, and dried product from the tooling fixture and place it on the coating fixture.

[0052] S6. Use radio frequency power to excite inert argon gas into plasma to perform plasma cleaning on the product.

[0053] S7. Place the coating fixture onto the coating tooling and install it into the process chamber of the coating equipment.

[0054] S8. Start the coating program. First, add 10 mL of KH-570 coupling agent for liquid evaporation to form a coupling agent layer on the product surface. Then, use 10 g of C-type Pyrelin for chemical vapor deposition coating. During the first hour of chemical vapor deposition, the deposition rate is 0.6 μm / h, the deposition rate is 0.7 μm / h during the next hour, and the deposition rate is 0.8 μm / h during the middle 4 hours. The deposition pressure is 12 mTorr.

[0055] S9. When the coating thickness reaches 3μm, the coating program is turned off;

[0056] S10. Remove the coating fixture, test the film thickness on the monitoring sheet. If the thickness is qualified, remove the product.

[0057] S11. Remove the masking adhesive;

[0058] S12. Inspect the appearance of the product. If the film layer is uniform and undamaged, it is considered qualified.

[0059] The UV adhesive mentioned is model speedmask 9-20479-B-REV A, purchased from DYMAX.

[0060] The aforementioned C-type Pyrelin is a commercially available product.

[0061] Comparative Example 1

[0062] This example provides a coating method for an underwater microphone, specifically the following steps:

[0063] S1. Check whether the diaphragm of the underwater microphone is damaged and whether the surface is clean. Select an underwater microphone with an undamaged diaphragm and a clean surface.

[0064] S2. Place the underwater microphone onto the tooling fixture;

[0065] S3. Using a high-precision dispensing machine, apply masking adhesive UV glue to the area that needs to be masked. The width of the adhesive coating is 0.2-0.3mm and the length is 3mm.

[0066] S4. Place in a UV curing oven for drying, curing, and shaping, with a curing wavelength of 400nm, a curing energy of 2000mJ, and a curing time of 10 seconds;

[0067] S5. Remove the cured, shaped, and dried product from the tooling fixture and place it on the coating fixture.

[0068] S6. Use radio frequency power to excite inert argon gas into plasma to perform plasma cleaning on the product.

[0069] S7. Place the coating fixture onto the coating tooling and install it into the process chamber of the coating equipment.

[0070] S8. Start the coating program. First, add 10 mL of KH-570 coupling agent to evaporate the liquid to the product surface to form a coupling agent layer. Use 10 g of C-type Pyrelin for chemical vapor deposition coating. During the first hour of chemical vapor deposition, the deposition rate is 0.6 μm / h, the deposition rate is 0.7 μm / h during the next hour, and the deposition rate is 0.8 μm / h during the middle 4 hours. The deposition pressure is 12 mTorr.

[0071] S9. When the coating thickness reaches 12μm, the coating program is turned off;

[0072] S10. Remove the coating fixture, test the film thickness on the monitoring sheet. If the thickness is qualified, remove the product.

[0073] S11. Remove the masking adhesive;

[0074] S12. Inspect the appearance of the product. If the film layer is uniform and undamaged, it is considered qualified.

[0075] The UV adhesive mentioned is model speedmask 9-20479-B-REV A, purchased from DYMAX.

[0076] The aforementioned C-type Pyrelin is a commercially available product.

[0077] Comparative Example 2

[0078] This example provides a coating method for an underwater microphone, specifically the following steps:

[0079] S1. Check whether the diaphragm of the underwater microphone is damaged and whether the surface is clean. Select an underwater microphone with an undamaged diaphragm and a clean surface.

[0080] S2. Place the underwater microphone onto the tooling fixture;

[0081] S3. Using a high-precision dispensing machine, apply masking adhesive sealant to the area that needs to be masked. The width of the adhesive coating is 0.4-0.7mm and the length is 3mm.

[0082] S4. Place in a constant temperature oven to dry at 60℃ for 60 minutes.

[0083] S5. Remove the cured, shaped, and dried product from the tooling fixture and place it on the coating fixture.

[0084] S6. Use radio frequency power to excite inert argon gas into plasma for plasma cleaning.

[0085] S7. Place the coating fixture onto the coating tooling and install it into the process chamber of the coating equipment.

[0086] S8. Start the coating program. First, add 10 mL of KH-570 coupling agent to evaporate the liquid to the product surface to form a coupling agent coating. Use 10 g of C-type Pyrelin for chemical vapor deposition coating. During the first hour of chemical vapor deposition, the deposition rate is 0.6 μm / h, the deposition rate is 0.7 μm / h during the next hour, and the deposition rate is 0.8 μm / h during the middle 4 hours. The deposition pressure is 12 mTorr.

[0087] S9. When the coating thickness reaches 3μm, the coating program is turned off;

[0088] S10. Remove the coating fixture, test the film thickness on the monitoring sheet. If the thickness is qualified, remove the product.

[0089] S11. Remove the masking adhesive;

[0090] S12. Inspect the appearance of the product. If the film layer is uniform and undamaged, it is considered qualified.

[0091] The sealant is designated as ITW CHEMASK CM8 solder resist.

[0092] The aforementioned C-type Pyrelin is a commercially available product.

[0093] A partial image of the underwater microphone obtained by the coating process in this example is shown below. Figure 1 As shown in the image, the red circle indicates that the Piriton membrane layer has ruptured, significantly affecting its protective effect.

[0094] Performance testing

[0095] Test method: Check whether the coated diaphragm is uniform and intact, and whether there is any corrosion or rust. Then, immerse the product in water to test the underwater microphone's sound pickup performance. Specific methods are as follows:

[0096] Vibration diaphragm integrity check: Visually inspect under a 1.45x microscope for any damage, cracks, or other defects.

[0097] Corrosion inspection: Neutral salt spray test. Devices with the pyrene film are placed in a salt spray test chamber. After 24 hours, they are examined under a microscope. No abnormalities, rust spots, or film peeling are observed in the film-covered area.

[0098] Salt spray test chamber parameters: temperature 33-35℃ constant temperature, solution: NaCl solution, concentration 45-55g / L.

[0099] Test subjects: underwater microphones coated in Example 1 and Comparative Examples 1-2. The test results are detailed in Table 1.

[0100] Table 1

[0101]

[0102]

Claims

1. A coating method for an underwater microphone, characterized in that, At least the following steps are included: S1. Check whether the diaphragm of the underwater microphone is damaged and whether the surface is clean. Select an underwater microphone with an undamaged diaphragm and a clean surface. S2. Place the underwater microphone onto the tooling fixture; S3. Use a high-precision dispensing machine to apply masking adhesive to the areas that need to be masked. S4. Place in a curing oven for drying, curing, and shaping; S5. Remove the cured, shaped, and dried product from the tooling fixture and place it on the coating fixture. S6. Perform plasma cleaning; S7. Place the coating fixture onto the coating tooling and install it into the process chamber of the coating equipment. S8. Start the coating program and use Piriton for chemical vapor deposition coating. S9. When the coating thickness reaches 2-5μm, turn off the coating program; S10. Remove the coating fixture, test the film thickness on the monitoring sheet. If the thickness is qualified, remove the product. S11. Remove the masking adhesive; S12. Inspect the appearance of the product. If the film layer is uniform and undamaged, it is qualified. The masking adhesive is a UV adhesive, and the coating width of the masking adhesive is 0.2-0.35mm, and the length is 2-3mm; The UV adhesive is acrylate urethane, with a viscosity of 100,000-150,000 cps at 25°C, an elongation of 100-300%, and a tensile strength of 2-5.5 psi. In step S8, the deposition rate of chemical vapor deposition is 0.1-1 μm / h, and the deposition pressure is 8-13 mTorr.

2. The coating method for an underwater microphone according to claim 1, characterized in that, The plasma cleaning method in step S6 includes: using an radio frequency power supply to excite inert gas into plasma to clean the product inside the coating fixture.

3. The coating method for an underwater microphone according to claim 2, characterized in that, The inert gas mentioned is argon.

4. The coating method for an underwater microphone according to claim 1, characterized in that, In step S8, after starting the coating process, a coupling agent is added and evaporated to deposit onto the product surface.

5. The coating method for an underwater microphone according to any one of claims 1-4, characterized in that, In step S8, the Parylene chemical vapor deposition is not uniform throughout. The deposition rate is 0.6 μm / h in the first 1-2 hours of chemical vapor deposition, 0.7 μm / h in the next 0.5-1 hours, and 0.8 μm / h in the middle 3-4 hours.

Images