Backplate assembly for condenser microphone

Abstract

The microphone assembly (100) includes a housing (107), a single flexible diaphragm (101), and a rigid backplate (102) that is coated with a parylene configured to help reduce flatness deviation of the backplate (102) across a diameter of the backplate. A plurality of openings (309) can extend from a top of the backplate (102) to a bottom of the backplate (102).

Description

Technical Field

[0001] The present disclosure generally relates to microphones, and more specifically to electret condenser microphone assemblies such as backplates manufactured with alternative electret materials.

[0002] Cross - Reference to Related Applications This application claims the benefit and priority of U.S. Patent Application No. 17 / 184,338, filed on February 24, 2021, the disclosure of which is hereby incorporated by reference in its entirety.

Background Art

[0003] A microphone converts sound into an electrical signal using a transducer that includes a diaphragm, converts sound into mechanical motion, and converts mechanical motion into an electrical signal. Generally, microphones can be classified by transducer type (e.g., condenser, dynamic, ribbon, carbon, laser, or micro - electro - mechanical systems (MEMS)). Condenser microphones are widely used in the audio, electronics, and instrumentation industries. An electret condenser microphone includes a flexible diaphragm or thin film and a rigid backplate that can include one or more apertures. The diaphragm or flexible diaphragm may be coated with an electret material.

[0004] In an electret condenser microphone, the diaphragm functions as one plate of the capacitor and the backplate functions as the other plate. Vibration changes the distance between the diaphragm and the backplate. The voltage held between the diaphragm and the backplate changes in response to vibrations in the air according to the capacitance formula (C = Q / V), where Q is the charge in coulombs, C is the capacitance in farads, and V is the potential difference in volts. This voltage change is amplified by an FET, and an audio signal appears at the output through a DC - blocking capacitor.

[0005] In some cases, the flexible diaphragm is coated with an electret material. In other cases, a rigid backplate (instead of the diaphragm) is coated with an electret material. The raw punched metal backplate can be coated with Teflon® or a Teflon® variant. A common method of applying this electret material to a metal backplate is by lamination. In this lamination process, the backplate may warp due to the high heat required for lamination. In certain examples, during the lamination process, the stress built into the raw punching metal backplate during the punching process is released, resulting in warping of the backplate.

[0006] By maintaining the flatness of the rigid backplate during manufacturing, the sensitivity of the microphone assembly can be kept constant. The cartridge bump of a condenser microphone is typically assembled to create an air gap of 1 / 1000 to 1 / 2000 inches between the diaphragm and the backplate. Even a deviation of the backplate by 6 / 10,000 to 8 / 10,000 inches can have a significant impact on the performance of the microphone assembly.

SUMMARY OF THE INVENTION

[0007] The following presents a simplified summary of the present disclosure in order to provide a basic understanding of some aspects of the present disclosure. This summary is not an extensive overview of the disclosure. Its purpose is not to identify key or critical elements of the disclosure nor to delineate the scope of the disclosure. The following summary merely presents some concepts of the present disclosure in a simplified form as a prelude to the more detailed description provided below.

[0008] The present disclosure solves many of the above problems with a microphone assembly that includes a perforated backplate assembly coated with an electret material such as a vapor deposited polymeric conformal coating material. In one example, the electret material is parylene (Registered Trademark)It may be. Different from the above laminate coating method, parylene is applied by a non-heating vapor deposition method. As a result, the parylene-coated backplate is very flat and contributes to ensuring the stable sensitivity of the microphone assembly.

[0009] The backplate includes a main body, an upper surface and a lower surface, and a plurality of through holes extending from the upper surface of the backplate to the lower surface of the backplate. In one embodiment, the upper surface of the backplate is coated with a vapor deposition polymer conformal coating material such as parylene. The main body of the backplate may be circular, rectangular, or other desired shapes. The main body of the backplate may be manufactured from raw punching metal, metallized ceramic, metallized plastic, or printed circuit board. In another embodiment, the plurality of inner diameters of the plurality of through holes are also coated with parylene.

[0010] These and other novel advantages, details, embodiments, features, and objects of the present disclosure will be apparent to those of ordinary skill in the art who are useful in interpreting the present disclosure from the following detailed description, claims, and drawings of the present disclosure.

Brief Description of the Drawings

[0011] A more complete understanding of the present disclosure and its advantages can be obtained by referring to the following description in consideration of the accompanying drawings, where the same reference numerals represent the same features, and where it can be obtained by referring to the following description.

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Figure 1

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Figure 2

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Figure 3

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Figure 3A

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Figure 3B

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Figure 5

MODE FOR CARRYING OUT THE INVENTION

[0019] In the following description of various examples, reference is made to the accompanying drawings which form a part of this specification and in which are shown by way of illustration various examples in which aspects may be practiced. References to "embodiments", "examples", etc. indicate that the embodiments or examples of the present disclosure so described may include particular features, structures, or characteristics, but each embodiment or example is not necessarily required to include the particular features, structures, or characteristics. Further, it is contemplated that a particular embodiment or example may have some, all, or none of the features described for other embodiments. It should also be understood that other embodiments and examples can be utilized and structural and functional changes can be made without departing from the scope of the present disclosure.

[0020] Unless otherwise stated, a series of adjectives used to describe components, such as "first", "second", "third", etc., are used only to indicate different components which may be similar components. However, the use of this consecutive adjective does not mean that the components must be provided in the order given in a temporal, spatial, sequential, or any other way.

[0021] Also, in this specification, various exemplary features and elements can be described using terms such as "front", "back", "side", etc. For convenience, these terms are used in this specification based on, for example, the exemplary directions shown in the drawings and / or the directions in typical use. Nothing in this specification should be construed as requiring that the structure have a specific three-dimensional or spatial direction in order to fall within the scope of the claims.

[0022] Condenser microphones are widely applied in the audio, electronics, and instrumentation industries. Condenser microphones can be either wired or wireless. In the wired case, these microphones can be connected to a transmitter or receiver via any of various cables including twisted pair cables, coaxial cables, or optical fibers. These wired microphones can also be connected to a transmitter or receiver using any of various connectors including LEMO connectors, XLR connectors, TQG connectors, TRS connectors, USB, or RCA connectors. Condenser microphones can also be wireless and are connected to an audio system by any of various protocols including WiMAX, LTE, Bluetooth, Bluetooth broadcast, GSM, 3G, 4G, 5G, Zigbee, 60 GHz Wi-Fi, Wi-Fi (e.g., compliant with IEEE 802.11a / b / g), or the NFC protocol. In this embodiment, the transmitter can be included within the microphone or connected to the microphone.

[0023] Referring to FIGS. 1 and 2, in one example, the present disclosure includes a microphone assembly 100 that includes a single flexible film or diaphragm 101 having a metallized coating separated from a backplate 102. A protective grill (not shown) may be attached over the diaphragm 101 to function as an environmental protection barrier. The diaphragm 101 is used as a sensing electrode of a capacitive electroacoustic transducer and is made of a known material used to form a microphone diaphragm, such as a metal film or a metallized polymer film.

[0024] The diaphragm 101 and the back plate 102 form a capacitor, which is also called a condenser. When a sound wave hits the diaphragm 101, the diaphragm moves, and the height of the air gap 103 between the diaphragm 101 and the back plate 102 changes. Due to this change in the gap, the capacitance of the capacitor formed by the diaphragm 101 and the back plate 102 changes. When a charge Q fixed or controlled on the capacitor is maintained, a voltage is formed across the capacitor, and this voltage changes in proportion to the change in the height of the air gap 103. Such a change in voltage is amplified by a transistor 115 that can be coupled to a printed circuit board 116. The audio signal appears at the output 117 as shown in FIG. 2. The transistor 115 can be configured as a field effect transistor (FET) or a bipolar junction transistor (BJT).

[0025] The diaphragm 101 is stretched over a diaphragm frame 104 and may be adhered or adhesively fixed to the diaphragm frame. The diaphragm frame 104 can hold tension on the diaphragm 101. The back plate 102 is rigid or fixed. The diaphragm 101 is spaced from the back plate 102 by a narrow air gap 103 (shown in FIG. 2) defined by spacers 105. The back plate 102 is, for example, made of raw punching metal. The spacers 105 are made of, for example, a rigid plastic insulating material, prevent deformation of the spacers 105 due to pressure, and prevent current from flowing between the diaphragm 101 and the back plate 102. The spacers can take on many shapes such as walls or ridges. The diaphragm 101, the back plate 102, and the spacers 105 can be coupled to a housing 107. The housing 107 may be made of metal. The housing 107 also functions as an electrical ground.

[0026] The diaphragm 101 and the back plate 102 can use various shapes and configurations. For example, in FIG. 1, the diaphragm frame 104 may be circular, and the back plate may also be circular. A person skilled in the art will understand that the diaphragm and the back plate can include other shapes according to the shapes of the housing 107 and other components of the present disclosure.

[0027] In some cases, the flexible diaphragm may be coated with an electret material. In other cases, the back plate may be coated with an electret material. Teflon (registered trademark) has been used as an electret material for decades. A common method of applying this electret material onto a base metal back plate is by lamination. However, in this lamination process, the back plate may warp due to the high heat required for lamination. Referring to FIG. 2 again, in one example, the air gap 103 may be 0.0015 inches (when the diaphragm is stationary). In another example, the air gap 103 may exceed 0.0015 inches. As the distance between the back plate and the diaphragm increases, i.e., the height of the air gap increases, it is necessary to increase the voltage required to maintain appropriate microphone sensitivity. Microphone sensitivity is the output voltage of the microphone divided by the magnitude of the air pressure disturbance. Even if the back plate warps by only 1 / 1000 of an inch, it can have a significant impact on the performance of the microphone assembly 100. For example, a Teflon (registered trademark)-coated back plate may, on average, have a deviation of about 46% of the total air gap height. Therefore, such flatness changes can lead to changes in capacitance and potentially to changes in the sensitivity of the microphone assembly 100. In some cases, the diaphragm may be electrostatically adsorbed to the back plate, collapse onto the back plate, and the microphone assembly 100 may malfunction. For this reason, the production volume may be suppressed.

[0028] Conversely, in one example, a polymer conformal coating material such as parylene can be used as the electret material and applied by a non-thermal vapor deposition method. Parylene is a generic term for members of a polymer series, and its monomer typically contains a p-phenylene diyl ring (benzene ring) and a 1,2-ethylene diyl bridge (aliphatic bridge). The basic member of this series is poly(p-xylylene) (parylene N), and its derivatives may contain other functional groups instead of specific hydrogen atoms present in the N monomer. FIG. 3a shows a backplate 102 having an electret coating 312. The backplate 102 can be configured to exhibit a flatness deviation of 10% of the total height of the air gap (while the diaphragm is stationary) when measured across the diameter of the backplate body 308. In one example, the backplate 102 having an electret coating 312 can be configured to exhibit a flatness deviation of 10% or less of the total height of the air gap (while the diaphragm is stationary) when measured across the diameter of the backplate body 308. In another example, the backplate 102 having an electret coating 312 can be configured to exhibit a flatness deviation between 10% and 20% of the total height of the air gap (while the diaphragm is stationary) when measured across the diameter of the backplate body 308. In yet another example, the backplate 102 having an electret coating 312 can be configured to exhibit a flatness deviation of less than 35% or less than 20% of the total height of the air gap (while the diaphragm is stationary) when measured across the diameter of the backplate body 308. In any of the foregoing examples, the flatness deviation of the backplate can be measured and confirmed using any number of dimensional measurement devices including, but not limited to, an optical three-dimensional measurement system, a machine vision system, a laser tracker, and an optical comparator. Thus, the parylene-coated backplate can contribute to maintaining the consistent sensitivity of the microphone assembly 100 during manufacturing and reducing the risk of diaphragm breakdown, thereby increasing the manufacturing yield.

[0029] Referring to FIGS. 3 and 3a, the backplate 102 includes a body 308 made of raw punching metal. The body 308 may include through holes or holes indicated by arrow 309. These openings allow air to pass from the upper surface 310 of the backplate to the lower surface 311 of the backplate. A vapor-deposited electret coating 312 may be present on the upper surface of the backplate body 308.

[0030] In one embodiment, the thickness of the electret coating 312 is 25 µm. In other embodiments, the thickness of the electret coating 312 may be less than 25 µm or greater than 25 µm. In one example, the vapor-deposited electret coating may be a cross-linked fluorinated derivative of parylene N known as poly(α,α,α’,α’-tetrafluoro-p-xylylene) (parylene-AF4). Parylene-AF4 is commercially available as Parylene HT®, a registered trademark of Specialty Coating Systems, and diX SF manufactured by Dai San Kasei Co., Ltd. Parylene-AF4 has high dielectric strength, low dielectric constant, the ability to deposit uniformly at room temperature, and high penetration ability. Other parylene derivatives and other carbon-fluorine-based polymers containing fluorinated parylene with less or more fluorine-hydrogen substitution than parylene-AF4 may also be potentially used as effective electret materials. Other types of polymer conformal coating materials that can be vapor-deposited can also be used.

[0031] A further advantage of coating the backplate 102 with the electret coating 312 is that the backplate coated with parylene exhibits an improved initial charge capacity before discharge. The initial charge capacity of the parylene-coated backplate before discharge is much higher than that of a Teflon®-laminated backplate. For example, the backplate 102 having the electret coating 312 can exhibit an initial charge capacity of about -1900 V before discharge, while an equivalent backplate laminated with Teflon® exhibits an initial charge capacity of about -1000 V before discharge.

[0032] Referring to FIG. 3b, the backplate body 308 may include through holes or apertures 309 as indicated at 309. These openings allow air to pass from the upper surface 310 of the backplate to the lower surface 311 of the backplate. A uniform electret coating 312 may be present on the upper surface 310 of the backplate body 308. Further, an electret coating 312 may be present on the inner diameter 314 of the through hole 309. This is advantageous for several reasons. Importantly, coating the inner diameter 314 of the through hole 309 with an electret can contribute to ensuring a more uniform charge distribution across the backplate body. This configuration also helps to mitigate problems associated with reading the backplate voltage during manufacturing and subsequent quality control stages, resulting in improved efficiency of manufacturing and quality control tests. In another example, the through hole 309 may be masked to prevent the inner diameter 314 from being coated with the electret coating 312.

[0033] As will be appreciated by those skilled in the art, the location, number, and size of through-holes or holes affect the audio characteristics of a microphone, such as frequency response and sensitivity. Any number of variations in the size and arrangement of the holes can also benefit from the vapor-deposited electret coating 312 of inner diameter 314. For example, when the diameter of the backplate ranges from several tens of millimeters to several millimeters, the holes in the backplate become proportionally smaller. For example, a backplate with a diameter of 0.120 inches or less may have holes of 0.020 inches or less. The current process configured to shear a Teflon® film layer along the edge of the through-hole may not be able to substantially remove holes in a backplate having a diameter of less than 0.020 inches. An exemplary process may include a 0.001-inch stainless steel shim that can be placed within a nest having a polyurethane plug below. The backplate may be placed on the shim with the polytetrafluoroethylene® laminate side facing the shim. There is a possibility that a press may push the backplate onto the shim at high pressure, at which point the urethane plug may liquefy and force may be applied to the shim. Since the urethane plug applies a constant pressure behind the shim, the shim may cut into the sharp edge of the backplate and trim excess Teflon®.

[0034] The above process may not be suitable for removing holes less than 0.020 inches in diameter. As a result, the flow of air through the holes in the backplate is restricted, and the microphone capsule may malfunction. Conversely, using a vapor-deposited polymer conformal coating such as parylene can be finely and uniformly applied in the vapor phase to the backplate, potentially eliminating the need to shear the conformal material layer from the holes. This enables the manufacture of smaller condenser electret microphone assemblies for various applications. Additionally, by using a vapor-deposited polymer conformal coating such as parylene as the electret material instead of Teflon®, the backplate manufacturing process can be simplified. Specifically, the above process may require manufacturing a backplate with sharp edges around the holes in the backplate so that the shim can shear off excess Teflon®. Such a limitation can be avoided by using a vapor-deposited polymer conformal coating such as parylene, thus simplifying the backplate manufacturing process and / or enabling an alternative backplate manufacturing process.

[0035] Alternative embodiments of the present disclosure are enabled by a thermal evaporation process. Unlike conventional lamination methods that require high heat, the vapor deposition coating process is performed in a low-heat environment. Thus, heat-sensitive materials and components can be used to manufacture the backplate assembly. This includes alternative raw backplate materials such as metallized plastics, metallized ceramics, and printed circuit boards. In this embodiment, referring again to FIGS. 3 and 4, the body 308 of the backplate 102 consists of a printed circuit board. The electret coating 312 is uniformly applied to the upper surface 310 of the backplate 102. The printed circuit board may include an amplifier circuit such as a field effect transistor or a bipolar junction transistor.

[0036] Another advantage of using a vapor-deposited polymer conformal coating, such as parylene, as an electret material is the manufacturing efficiency associated with the vapor deposition process. In conventional lamination processes, the production volume has been severely limited. In some cases, with current lamination processes, only a few dozen backplates can be laminated at a time. In contrast, the vapor deposition process can increase the production volume by at least a factor of 10. For example, a large deposition chamber can accommodate hundreds or thousands of parts, so hundreds of backplates can be coated with parylene at a time.

[0037] Referring to FIG. 5, the substrate 515 is placed within the deposition chamber 521 for coating. A variety of substrates can be used, including metals, plastics, metallized plastics, metallized ceramics, elastomers, silicon, and silicon-based derivatives. The dimer 516 is then placed into the evaporation chamber 517. Many different types of dimers can be used. The dimer 516 is vaporized into the dimer gas 518. The dimer gas 518 enters the pyrolysis furnace 519, where it is heated and converted into the monomer gas 520. The monomer gas 520 enters the deposition chamber 521 at ambient temperature and polymerizes the exposed surface of the substrate 515. In one example, when the exposed surface of the substrate 515 is coated with parylene, no additional curing step is required. The thickness of the parylene coating can range from 1 μm to hundreds of μm.

[0038] The microphone assembly may include a housing including an upper portion and a lower portion, the housing may further include a flexible diaphragm positioned above the backplate assembly, and a spacer interposed between the diaphragm and the backplate assembly. An air gap may be created between the diaphragm and the backplate by the spacer. The backplate assembly may be coupled to the housing. The backplate assembly may further include a body including a diameter, an upper surface, and a lower surface. A coating of a vapor-deposited electret material may cover the upper surface of the body, and the body may exhibit a flatness deviation across the entire diameter of the body configured to contribute to preventing the diaphragm from collapsing onto the backplate assembly. The flatness deviation across the diameter of the body may be 10% or less of the height of the air gap. The backplate assembly may also include a plurality of through-holes that can extend from the upper surface of the body to the lower surface of the body, and a coating of vapor-deposited parylene may cover the plurality of inner diameters of the plurality of through-holes, and the coating of vapor-deposited parylene may be configured to facilitate ensuring a uniform charge distribution across the entire backplate assembly body. The signal amplification circuit may be disposed under the backplate assembly and may be connected to the backplate and a plurality of output lead wires extending from the bottom of the housing. The body of the backplate may include raw punching metal, a printed circuit board, metallized plastic, or metallized ceramic. The coating of the vapor-deposited electret material may be at least 20 μm thick. Further, the backplate may exhibit a maximum initial charge capacity of -1900V.

[0039] The backplate assembly for a condenser microphone may include a body. The body may include a diameter, an upper surface, a lower surface, and a plurality of through holes extending from the upper surface of the body to the lower surface of the backplate. A coating of vapor-deposited parylene may be coated on the upper surface of the body and the plurality of inner diameters of the plurality of through holes. The coating of vapor-deposited parylene may be configured to contribute to ensuring a uniform charge distribution across the backplate assembly. The body of the perforated backplate assembly may have a flatness deviation of 20% or less of the air gap height that can be interposed between the diaphragm and the backplate assembly across the diameter of the body. The backplate can achieve a maximum initial charge capacity of -1900 volts. The body of the perforated backplate may include unprocessed punching metal, a printed circuit board, metallized plastic, or metallized ceramic.

[0040] The backplate assembly for a condenser microphone may include a body that may include a diameter and an upper surface. A vapor-deposited parylene coating may be coated on the body. The body may have a flatness deviation of 10% or less of the height of the air gap that can be interposed between the diaphragm and the perforated backplate assembly across the diameter of the body. The coating of vapor-deposited parylene may coat the plurality of inner diameters of the plurality of through holes that can extend from the upper surface of the body through the lower surface of the backplate. The coating of vapor-deposited parylene may be configured to contribute to ensuring a uniform charge distribution across the backplate assembly.

[0041] The coating of the vapor-deposited electret material on both the upper surface of the backplate body and the plurality of inner diameters of the plurality of perforations may include parylene-AF4.

[0042] In the foregoing specification, the disclosure has been described with reference to its specific exemplary embodiments. Although the disclosure has been described in accordance with preferred embodiments, those skilled in the art will recognize that various modifications, embodiments, or changes of the disclosure may be practiced within the spirit and scope of the disclosure as set forth in the appended claims. Accordingly, the specification and drawings are to be regarded in an illustrative rather than a limiting sense. Therefore, except as may be required in view of the claims, it is not intended to limit the disclosure.

Claims

1. A backplate assembly for a condenser microphone, comprising a body, the body having a diameter, an upper surface, and a lower surface and being coated on the upper surface thereof with a coating of vapor-deposited parylene (registered trademark) electret material, the coating of the vapor-deposited parylene electret material being configured to contribute to ensuring a uniform charge distribution across the entire body of the backplate assembly.

2. The backplate assembly according to claim 1, wherein the body has a flatness deviation of 20 percent or less of the height of the air gap intervening between the diaphragm and the backplate assembly across the entire diameter of the body.

3. The backplate assembly according to claim 1, wherein the coating of the vapor-deposited parylene electret material comprises parylene-AF4.

4. The backplate assembly according to claim 1, wherein the backplate assembly exhibits a maximum initial charge capacity of -1900 volts.

5. The backplate assembly according to claim 1, wherein the body of the backplate assembly comprises a printed circuit board.

6. The backplate assembly according to claim 1, wherein the body of the backplate assembly comprises metallized plastic.

7. The backplate assembly according to claim 1, wherein the body of the backplate assembly comprises metallized ceramic.

8. The backplate assembly according to claim 1, further comprising a plurality of through holes extending from the upper surface to the lower surface of the body.

9. The coating of the vapor-deposited parylene electret material covers the plurality of inner diameters of the plurality of through holes, the backplate assembly according to claim 8.

10. The vapor-deposited parylene electret material contains non-fluorinated parylene, the backplate assembly according to claim 1.

11. The non-fluorinated parylene contains parylene N, the backplate assembly according to claim 10.

12. A backplate assembly for a condenser microphone, including a body, the body having a diameter, and an upper surface and including a coating of a vapor-deposited parylene electret material covering the upper surface of the body, the body having a flatness deviation of 10% or less of the height of the air gap intervening between the diaphragm and the backplate assembly over the entire diameter of the body, the backplate assembly.

13. The coating of the vapor-deposited parylene electret material contains parylene-AF4, the backplate assembly according to claim 12.

14. The body of the backplate assembly includes a printed circuit board, the backplate assembly according to claim 12.

15. The body of the backplate assembly includes metallized plastic, the backplate assembly according to claim 12.

16. The body of the backplate assembly includes metallized ceramic, the backplate assembly according to claim 12.

17. The backplate assembly according to claim 12 further includes a plurality of through holes extending from the upper surface of the body to the lower surface of the body. Claim 18 The coating of the vapor-deposited parylene electret material covers the plurality of inner diameters of the plurality of through holes, and the backplate assembly according to claim 17. Claim 19 The vapor-deposited parylene electret material contains non-fluorinated parylene, and the backplate assembly according to claim 12. Claim 20 The non-fluorinated parylene contains parylene N, and the backplate assembly according to claim 19.

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