Parylene Electret Condenser Microphone Backplate

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 relates generally to microphones, and more particularly to electret condenser microphone assemblies, such as backplates, made from alternative electret materials.

[0002] CROSS-REFERENCE TO RELATED APPLICATIONS This application claims priority to and the benefit of U.S. patent application Ser. No. 17 / 184,338, filed Feb. 24, 2021, the disclosure of which is incorporated herein by reference in its entirety. [Background technology]

[0003] A microphone uses a transducer that includes a diaphragm to convert sound into an electrical signal, convert sound into mechanical motion, and convert mechanical motion into an electrical signal. In general, microphones can be classified by the transducer type (e.g., capacitor, dynamic, ribbon, carbon, laser, or microelectromechanical systems (MEMS)). Condenser microphones are widely used in the audio, electronics, and instrumentation industries. An electret condenser microphone includes a flexible diaphragm or membrane and a rigid backplate that may contain one or more openings. The diaphragm or flexible diaphragm may be coated with an electret material.

[0004] In an electret condenser microphone, the diaphragm acts as one plate of a capacitor and the backplate acts as the other plate. Vibrations change the distance between the diaphragm and the backplate. The voltage maintained 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 charge, C is capacitance, and V is potential difference. This voltage change is amplified by the FET and the audio signal appears at the output via a DC blocking capacitor.

[0005] In some cases, the flexible diaphragm is coated with the electret material. In other cases, the rigid backplate (instead of the diaphragm) is coated with the electret material. A raw punched metal backplate can be coated with a coating of Teflon or a Teflon variant. A common method of applying this electret material to a metal backplate is by lamination. This lamination process can cause the backplate to warp due to the high heat required for lamination. In certain instances, the lamination process releases stresses that were built into the raw punched metal backplate during the hole drilling process, resulting in warping of the backplate.

[0006] Maintaining a consistent flatness of the rigid backplate during manufacturing ensures consistent sensitivity of the microphone assembly. Cartridges on condenser microphones are typically assembled with an air gap between the diaphragm and the backplate of 1-2000ths of an inch. Even a backplate that is misaligned by just 6-8 thousandths of an inch can significantly affect the performance of the microphone assembly. Summary of the Invention

[0007] The following presents a simplified summary of the disclosure in order to provide a basic understanding of some aspects of the disclosure. This summary is not an extensive overview of the disclosure. It is not intended to identify key or key elements of the disclosure, nor is it intended to delineate the scope of the disclosure. The following summary is merely intended to present some concepts of the 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 may be parylene. Parylene is applied by a non-thermal vapor deposition method, as opposed to the laminate application method described above. As a result, the parylene-coated backplate is very flat, helping to ensure consistent sensitivity of the microphone assembly.

[0009] The backplate includes a body, an upper surface and a lower surface, and a number 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-deposited polymeric conformal coating material, such as parylene. The backplate body may be circular, rectangular, or any other desired shape. The backplate body may be fabricated from raw punched metal, metallized ceramic, metallized plastic, or printed circuit board. In another embodiment, the inner diameters of the number 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 skilled in the art who have utility in interpreting the present disclosure from the following detailed description of the disclosure, claims, and drawings. [Brief description of the drawings]

[0011] A more complete understanding of the present disclosure and its advantages may be obtained by reference to the following description in consideration of the accompanying drawings, in which like reference characters represent like features, and in which:

[0012] [Figure 1] FIG. 1 is a perspective exploded view of a first example microphone condenser assembly according to the present disclosure.

[0013] [Diagram 2] 2 is a cross-sectional view of a portion of the microphone condenser assembly shown in FIG. 1.

[0014] [Diagram 3] FIG. 2 is a plan view of a first example of a back plate according to the present invention.

[0015] [Figure 3A] FIG. 4 is a cross-sectional view of the first example shown on line 3a / 3b in FIG.

[0016] [Figure 3B] FIG. 4 is a cross-sectional view of the second example shown on line 3a / 3b in FIG.

[0017] [Figure 4] FIG. 13 is a plan view of a third example of a backplate according to the present disclosure.

[0018] [Diagram 5] 1 illustrates a deposition process. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

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

[0020] Unless otherwise noted, sequential adjectives such as "first," "second," "third," etc., used to describe elements are used only to indicate different elements that may be similar elements. However, the use of the sequential adjectives does not imply that the elements must be presented in the given order, temporally, spatially, sequentially, or in any other way.

[0021] Also, although various exemplary features and elements may be described herein using terms such as "front," "back," "side," and the like, for convenience, these terms are used herein based on, for example, exemplary orientations shown in the drawings and / or orientations in typical use. Nothing in this specification should be construed as requiring that structures have a particular three-dimensional or spatial orientation 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 may be wired or wireless. If wired, these microphones may be connected to a transmitter or receiver via any of a variety of cables including twisted pair, coaxial cable or optical fiber. These wired microphones may also be connected to a transmitter or receiver using any of a variety of connectors including LEMO connectors, XLR connectors, TQG connectors, TRS connectors, USB or RCA connectors. Condenser microphones may be wireless and connected to an audio system via any of a variety of protocols including WiMAX, LTE, Bluetooth, Bluetooth Broadcast, GSM, 3G, 4G, 5G, Zigbee, 60GHz Wi-Fi, Wi-Fi (e.g., IEEE 802.11a / b / g compatible), etc., or NFC protocols. In this embodiment, a transmitter may be included within or connected to the microphone.

[0023] 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 metalized coating separated from a backplate 102. A protective grill (not shown) may be attached over the diaphragm 101 to act as an environmental protection barrier. The diaphragm 101 is used as a sensing electrode for a capacitive electro-acoustic transducer and is made of known materials used to construct microphone diaphragms, such as metal films and metalized polymer films.

[0024] The diaphragm 101 and the backplate 102 form a capacitor, also called a condenser. When a sound wave strikes the diaphragm 101, it moves, changing the height of the air gap 103 between the diaphragm 101 and the backplate 102. This change in gap changes the capacitance of the capacitor formed by the diaphragm 101 and the backplate 102. When a fixed or controlled charge Q is maintained on the capacitor, a voltage is formed across the capacitor, which changes in proportion to the change in the height of the air gap 103. This change in voltage is amplified by a transistor 115, which can be coupled to a printed circuit board 116. The audio signal appears at an 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 tensioned on a diaphragm frame 104 and may be glued or adhesively fixed to the diaphragm frame. The diaphragm frame 104 may hold the diaphragm 101 in tension. The backplate 102 may be rigid or fixed. The diaphragm 101 is separated from the backplate 102 by a narrow air gap 103 (shown in FIG. 2) defined by a spacer 105. The backplate 102 may be made of, for example, raw punched metal. The spacer 105 may be made of, for example, a hard plastic insulating material, to prevent deformation of the spacer 105 under pressure and to prevent current flow between the diaphragm 101 and the backplate 102. The spacer may take a number of shapes, such as a wall or a ridge. The diaphragm 101, the backplate 102, and the spacer 105 may be coupled to a housing 107. The housing 107 may be made of metal. The housing 107 also serves as an electrical ground.

[0026] The diaphragm 101 and backplate 102 can use a variety of shapes and configurations. For example, in Figure 1, the diaphragm frame 104 can be circular and the backplate can also be circular. Those skilled in the art will appreciate that the diaphragm and backplate can include other shapes, depending on the shape of the housing 107 and other components of the disclosure.

[0027] In some cases, the flexible diaphragm may be coated with an electret material. In other cases, the backplate may be coated with an electret material. Teflon has been used as an electret material for decades. A common way to apply this electret material onto a base metal backplate is by lamination. However, this lamination process can cause the backplate to warp due to the high heat required for lamination. Referring again to FIG. 2, in one example, the air gap 103 may be 0.0015 inches (when the diaphragm is at rest). In another example, the air gap 103 may be greater than 0.0015 inches. As the spacing between the backplate and the diaphragm increases, i.e., the height of the air gap increases, a higher voltage must be required to maintain adequate microphone sensitivity. Microphone sensitivity is the microphone output voltage divided by the magnitude of the air pressure disturbance. Even a distortion of the backplate by just a thousandth of an inch can significantly affect the performance of the microphone assembly 100. For example, a Teflon coated backplate may have, on average, a deviation of about 46% of the total air gap height. Such changes in flatness may therefore lead to changes in capacitance and therefore sensitivity of the microphone assembly 100. In some cases, the diaphragm may be electrostatically attracted to the backplate and collapse onto the backplate, causing failure of the microphone assembly 100. This may limit production yields.

[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 deposition method. Parylene is a generic name for members of a polymer series whose monomers typically contain a p-phenylenediyl ring (a benzene ring) and a 1,2-ethylenediyl bridge (a fatty bridge). The basic member of this series is poly(p-paraxylylene) (parylene N), whose derivatives may contain other functional groups in place of certain 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 at rest) when measured across the diameter of the backplate body 308. In one example, the backplate 102 with the electret coating 312 may be configured to exhibit a flatness deviation of 10% or less of the total height of the air gap (while the diaphragm is at rest) when measured across the diameter of the backplate body 308. In another example, the backplate 102 with the electret coating 312 may be configured to exhibit a flatness deviation of between 10% and 20% of the total height of the air gap (while the diaphragm is at rest) when measured across the diameter of the backplate body 308. In yet another example, the backplate 102 with the electret coating 312 may 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 at rest) when measured across the diameter of the backplate body 308. In any of the foregoing examples, the flatness deviation of the backplate may be measured and confirmed using any number of dimensional measurement devices, including, but not limited to, optical three-dimensional measurement systems, machine vision systems, laser trackers, and optical comparators. Thus, the parylene coated backplate can help maintain consistent sensitivity of the microphone assembly 100 during manufacturing and reduce the risk of diaphragm collapse, thereby increasing manufacturing yields.

[0029] 3 and 3a, the backplate 102 includes a raw punched metal body 308. The body 308 may include through holes or apertures indicated by arrows 309. These openings allow the passage of air 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 electret coating 312 has a thickness of 25 m. In other embodiments, the electret coating 312 may have a thickness less than 25 m or greater than 25 m. In one example, the deposited electret coating may be a crosslinked 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, Inc., and diX SF, manufactured by Daisan Kasei Co., Ltd. Parylene-AF4 has high dielectric strength, low dielectric constant, and the ability to deposit uniformly at room temperature and high penetration capabilities. Additionally, other parylene derivatives and other carbon-fluorine based polymers, including fluorinated parylenes with less or more fluorine-hydrogen substitution than Parylene-AF4, may also be effective electret materials. Other types of polymeric conformal coating materials that can be deposited may also be used.

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

[0032] Referring to FIG. 3b, the backplate body 308 may include through holes or holes, indicated at 309. These openings allow the passage of air from the upper surface 310 of the backplate to the lower surface 311 of the backplate. A uniform deposited electret coating 312 may be present on the upper surface 310 of the backplate body 308. Additionally, 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 may contribute to ensuring a more uniform charge distribution across the backplate body. This configuration also helps to reduce issues associated with reading the backplate voltage during manufacturing and at the quality control stage thereafter, resulting in improved efficiency of manufacturing and quality control testing. 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 one skilled in the art will appreciate, the location, number, and size of the through holes or holes will affect the audio characteristics of the microphone, such as frequency response and sensitivity. Any number of variations in hole size and placement may also benefit from the vapor-deposited electret coating 312 on the inner diameter 314. For example, backplates with diameters of tens to several millimeters will have correspondingly smaller holes in the backplate. For example, backplates with diameters of 0.120 inches or less may have holes of 0.020 inches or less. Current processes configured to shear the Teflon film layer along the edges of the through holes may not be able to substantially remove holes in the backplate with diameters less than 0.020 inches. An exemplary process may include a 0.001 inch stainless steel shim that may be placed in a nest with a polyurethane plug underneath. The backplate may be placed on the shim with the polytetrafluoroethylene laminate side facing the shim. A press may press the backplate into the shim with high pressure, at which point the urethane plug may liquefy and exert a force on the shim. The urethane plug exerts constant pressure behind the shim, which can cause the shim to cut into the sharp edge of the backplate and trim off excess Teflon.

[0034] The above process may not be suitable for removing holes smaller than 0.020 inches in diameter. As a result, airflow through the backplate holes may be restricted, causing the microphone capsule to fail. Conversely, the use of a vapor-deposited polymer conformal coating, such as Parylene, may be finely and uniformly applied to the backplate in the vapor phase, eliminating the need to shear a layer of conformal material through the holes. This may allow for the production of smaller condenser electret microphone assemblies for use in a variety of applications. Additionally, the use of a vapor-deposited polymer conformal coating, such as Parylene, as the electret material instead of Teflon may simplify the backplate manufacturing process. Specifically, the above process may require the production of backplates with sharp edges around the perimeter of the backplate holes to allow shims to shear off the excess Teflon. Such limitations may be avoided by using a vapor-deposited polymer conformal coating, such as Parylene, thus simplifying and / or enabling alternative backplate manufacturing processes.

[0035] An alternative embodiment of the present disclosure is made possible by a non-thermal evaporation process. Unlike traditional lamination methods that require high heat, the evaporation 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 metalized plastics, metalized ceramics, and printed circuit boards. In this embodiment, referring again to FIGS. 3 and 4, the body 308 of the backplate 102 is made of a printed circuit board. An electret coating 312 is applied uniformly to the top surface 310 of the backplate 102. The printed circuit board may include amplifying circuitry such as field effect transistors or bipolar junction transistors.

[0036] Another advantage of utilizing a vapor-deposited polymer conformal coating such as parylene as an electret material is the manufacturing efficiencies associated with the vapor deposition process. Traditional lamination processes are severely limited in production volume. In some cases, current lamination processes can only laminate a few dozen backplates at a time. Conversely, a vapor deposition process can increase production volume by at least ten-fold. For example, hundreds of backplates can be coated with parylene at one time, since a large deposition chamber can accommodate hundreds or thousands of parts.

[0037] Referring to FIG. 5, the substrate 515 is placed in a 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 then enters an evaporation chamber 517. Many different types of dimers can be used. The dimer 516 is vaporized into a dimer gas 518. The dimer gas 518 enters a pyrolysis furnace 519 where it is heated and converted into a monomer gas 520. The monomer gas 520 enters the deposition chamber 521 at ambient temperature, polymerizing the exposed surface of the substrate 515. In one example, once the exposed surface of the substrate 515 is coated with parylene, no additional curing step is required. The thickness of the parylene coating may 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 located above the backplate assembly and a spacer interposed between the diaphragm and the backplate assembly. The spacer may create an air gap between the diaphragm and the backplate. 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 deposited electret material may cover the upper surface of the body, and the body may exhibit a flatness deviation across the diameter of the body configured to contribute to preventing the diaphragm from collapsing into 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 may extend from the upper surface of the body to the lower surface of the body, and a coating of deposited parylene may cover a plurality of inner diameters of the plurality of through holes, and the coating of deposited parylene may be configured to facilitate ensuring a uniform charge distribution across the backplate assembly body. A signal amplification circuit may be disposed beneath the backplate assembly and connected to the backplate and to a plurality of output leads extending from the bottom of the housing. The body of the backplate may comprise raw punched metal, a printed circuit board, a metallized plastic, or a metallized ceramic. The coating of vapor deposited electret material may be at least 20 μm thick. Additionally, 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 evaporated parylene may be applied to the upper surface of the body and to the inner diameters of the plurality of through holes. The coating of evaporated parylene may be configured to help ensure uniform charge distribution across the backplate assembly. The body of the perforated backplate assembly may have a flatness deviation across the diameter of the body of 20% or less of the height of an air gap that may be interposed between the diaphragm and the backplate assembly. The backplate may achieve a maximum initial charge capacity of -1900 volts. The body of the perforated backplate may include raw punched metal, printed circuit board, metallized plastic, or metallized ceramic.

[0040] A 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 deposited on the body. The body may have a flatness deviation across the diameter of the body of 10% or less of the height of an air gap that may be interposed between the diaphragm and the perforated backplate assembly. The vapor-deposited parylene coating may coat a plurality of inner diameters of a plurality of through holes that may extend from a top surface of the body through a bottom surface of the backplate. The vapor-deposited parylene coating may be configured to help ensure a uniform charge distribution across the backplate assembly.

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

[0042] In the foregoing specification, the present disclosure has been described with reference to its specific exemplary embodiment. Although the present disclosure has been described according to a preferred embodiment, those skilled in the art will recognize that various modifications, embodiments, or changes of the present disclosure may be made within the spirit and scope of the present disclosure as described in the appended claims. Therefore, the specification and drawings should be regarded in an illustrative sense, not a restrictive sense. Therefore, it is not intended to limit the disclosure except as may be necessary in light of the claims.

Claims

1. 1. A backplate assembly for a condenser microphone, comprising: a body, the body comprising: The diameter, The top surface and Underside and Including, a coating of vapor deposited parylene electret material covering the top surface of the body; A backplate assembly, wherein the coating of vapor-deposited parylene electret material is configured to contribute to ensuring a uniform charge distribution across a body of the backplate assembly.

2. 2. The backplate assembly of claim 1, wherein the body has a flatness deviation across a diameter of the body of no more than 20 percent of the height of an air gap between a diaphragm and the backplate assembly.

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

4. The backplate assembly of claim 1 , wherein the coating of vapor-deposited parylene electret material comprises parylene-VT4.

5. The backplate assembly of claim 1 , wherein the backplate assembly exhibits a maximum initial charge capacity of −1900 volts.

6. The backplate assembly of claim 1 , wherein a body of the backplate assembly includes a printed circuit board.

7. The backplate assembly of claim 1 , wherein a body of the backplate assembly comprises metallized plastic.

8. The backplate assembly of claim 1 , wherein a body of the backplate assembly comprises a metallized ceramic.

9. The backplate assembly of claim 1 , further comprising a plurality of through holes extending from the top surface of the body to the bottom surface of the body.

10. The backplate assembly of claim 9 , wherein the coating of vapor-deposited parylene electret material covers inner diameters of the through-holes.

11. The backplate assembly of claim 10, wherein the coating of vapor-deposited parylene electret material comprises parylene-VT4.

12. The backplate assembly of claim 1 , wherein the vapor-deposited parylene electret material comprises non-fluorinated parylene.

13. 13. The backplate assembly of claim 12, wherein the non-fluorinated parylene comprises at least one of Parylene N, Parylene C, or Parylene D.

14. 1. A backplate assembly for a condenser microphone, comprising: a body, the body comprising: The diameter, Top and Including, a coating of vapor deposited parylene electret material covering the top surface of the body; A backplate assembly, wherein the body has a flatness deviation across a diameter of the body of no more than 10 percent of the height of an air gap between a diaphragm and the backplate assembly.

15. The backplate assembly of claim 14, wherein the coating of vapor-deposited parylene electret material comprises parylene-AF4.

16. The backplate assembly of claim 14, wherein the coating of vapor-deposited parylene electret material comprises parylene-VT4.

17. The backplate assembly of claim 14 , wherein a body of the backplate assembly includes a printed circuit board.

18. The backplate assembly of claim 14 , wherein a body of the backplate assembly comprises metallized plastic.

19. The backplate assembly of claim 14 , wherein a body of the backplate assembly comprises a metallized ceramic.

20. The backplate assembly of claim 14 , further comprising a plurality of through holes extending from the top surface of the body to the bottom surface of the body.

21. 21. The backplate assembly of claim 20, wherein the coating of vapor-deposited parylene electret material covers inner diameters of the through-holes.

22. 22. The backplate assembly of claim 21, wherein the coating of vapor-deposited parylene electret material comprises parylene-VT4.

23. The backplate assembly of claim 14 , wherein the vapor-deposited parylene electret material comprises non-fluorinated parylene.

24. 24. The backplate assembly of claim 23, wherein the non-fluorinated parylene comprises at least one of Parylene N, Parylene C, or Parylene D.

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