Abstract:
An Electret Condenser Microphone (ECM) motor apparatus includes a diaphragm ring support structure, a charge plate, and at least one stitch. The diaphragm ring support structure defines an opening there through. The charge plate is disposed within the opening. The at least one stitch is coupled to the diaphragm ring support structure to the charge plate. The diaphragm is disposed adjacent to and in a generally parallel relationship to the charge plate. The stitch is configured to hold the charge plate and the diaphragm ring, and the stitch is configured to maintain a constant or nearly constant distance between the charge plate and the diaphragm in the absence of sound energy.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This patent claims benefit under 35 U.S.C. §119 (e) to U.S. Provisional Application No. 61822590 entitled “Apparatus for Securing Components in an Electret Condenser (ECM)” filed May 13, 2013, the content of which is incorporated herein by reference in its entirety. 
     
    
     TECHNICAL FIELD 
       [0002]    This application relates to acoustic devices and, more specifically, securing the internal components of these devices. 
       BACKGROUND OF THE INVENTION 
       [0003]    Various types of acoustic devices exist and one such type of device is a microphone. In one example, the Electret Condenser Microphone (ECM) is being used in devices such as cellular phones, video cameras, studio performance microphones, and headphones to mention a few examples. 
         [0004]    In the case of an ECM, sound energy enters through a sound port and vibrates a diaphragm and this action creates a corresponding change in electrical potential (voltage) between the diaphragm and a charge plate disposed near the diaphragm. This voltage represents the sound energy that has been received. Typically, the voltage is then transmitted to an electric circuit (e.g., an integrated circuit such as an application specific integrated circuit (ASIC)). Further processing of the signal may be performed on the electrical circuit. For instance, amplification or filtering functions may be performed on the voltage signal at the integrated circuit. 
         [0005]    In order for the diaphragm and charge plate combination to function properly, they need to be secured within the microphone. If, for example, the distance separating them changes in unexpected way (in the absence of the diaphragm moving in response to sound energy), then the microphone will not function properly. There are various methods to secure the diaphragm to the charge plate and the diaphragm to the housing. The connection between the charge plate and diaphragm provides mechanical support and is sometimes referred to as a “stitch”, due to its shape. The connection between the diaphragm and housing provides mechanical support and an air-tight seal around the perimeter of the diaphragm. Various attempts have been made to provide mechanical support and an air-tight seal, but these attempts have various shortcomings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0006]    For a more complete understanding of the disclosure, reference should be made to the following detailed description and accompanying drawings wherein: 
           [0007]      FIG. 1  comprises a side cutaway view of an ECM showing a stitch according to various embodiments of the present invention; 
           [0008]      FIG. 2  comprises a perspective view of an ECM with a stitch according to various embodiments of the present invention; 
           [0009]      FIG. 3  comprises a top view of an ECM with a stitch according to various embodiments of the present invention; and 
           [0010]      FIG. 4  comprises a flow chart for making an ECM with a stitch according to various embodiments of the present invention. 
       
    
    
       [0011]    Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity. It will further be appreciated that certain actions and/or steps may be described or depicted in a particular order of occurrence while those skilled in the art will understand that such specificity with respect to sequence is not actually required. It will also be understood that the terms and expressions used herein have the ordinary meaning as is accorded to such terms and expressions with respect to their corresponding respective areas of inquiry and study except where specific meanings have otherwise been set forth herein. 
       DETAILED DESCRIPTION 
       [0012]    Approaches are provided herein that allow elements of an acoustic device to be attached together. In particular, a stitch, typically comprised of epoxy, is used to hold a charge plate and a diaphragm and to, in the absence of sound energy, maintain a constant or substantially constant distance between these elements. 
         [0013]    Approaches are provided herein that allow elements of an acoustic device to be acoustically sealed. In particular, sealing material, typically comprised of epoxy, is applied around the perimeter of a diaphragm to create an air-tight seal around its perimeter. 
         [0014]    In one advantage of the present approaches, a stitch or other securing device can be made of a smaller size and this allows for smaller microphones and more available back volume; hence, more microphone sensitivity is provided. This is particularly advantageous for situations where the microphone needs to be as small as possible (e.g., in portable electronic devices and hearing aid applications). 
         [0015]    In another advantage, consistently sized and shaped stitches are obtained. This allows for less variation in the available back volume of microphones; hence, less sensitivity variation of the microphone. 
         [0016]    The present approaches also provide for increased mechanical strength than adhesive only stitches, specifically amongst its motor components. This allows for better mechanical performance when mechanical shocks impact the microphone. 
         [0017]    The present approaches also provide for reduced vibration sensitivity capability. In other words, the thickness of the stitch can be increased more precisely than epoxy only stitches, which reduces vibration sensitivity. 
         [0018]    In still another advantage of the present approaches, manual epoxy stitch “artistry” requirements are eliminated. In other words, operator dependency is alleviated; thus, less variation in the sensitivity of the microphone. 
         [0019]    In many of these embodiments, a motor includes a diaphragm and a charge plate. The diaphragm is separated from the charge plate by a constant distance. The separation is secured using a stitch that is constructed from a b-stage epoxy bonded to a polyimide layer, such as Kapton (manufactured by Dupont corporation). 
         [0020]    Referring now to  FIG. 1  and  FIG. 2 , and acoustic apparatus  100  is described. In this example, the acoustic apparatus is a motor for an ECM. The apparatus  100  includes a charge plate  102 , a diaphragm  104 , a diaphragm ring  106 , and a stitch  108 . In this example, these components are together referred to as an ECM motor. 
         [0021]    The charge plate  102  is a conventional charge plate that is used in ECMs and the diaphragm  104  is a conventional diaphragm (e.g., a film material) used in ECM devices. The ring  106  secures the diaphragm  104 . The charge plate  102  and diaphragm  104  are separated by a distance “d.” In the absence of sound energy, this distance d is maintained to be a constant distance or a nearly constant distance. 
         [0022]    The stitch  108  is, in one example, constructed of “b-stage” epoxy  107  backed with a polyimide film  109 . The polyimide (e.g., Kapton) film remains stable in a wide range of temperatures (e.g., from approximately −273 to approximately +400 degrees C.). The polyimide gives the b-stage epoxy a more sturdy mechanical structure, which makes for ease of shape designing, cutting, and handling with reduced risk of breakage and shape deformation. The b-stage epoxy bonds to the charge plate and adjacent diaphragm ring  106  to secure the motor. 
         [0023]    The b-staged epoxy used in the stitch  108  is a semi-solid form of partially cured epoxy. It is used between (e.g., midway between) the liquid state of blended, but partially cured resins, and a final state of a fully formed polymer. “B-stage” epoxy has been heat cured for a short period of time and then cooled (quenched) to prevent complete polymerization of the resin system. As discussed elsewhere herein, this midway solid state can expand manufacturing options. B-stage epoxy can be provided in a number of options such as in rolls or sheets. 
         [0024]    With the epoxy having been partially cured (e.g., less than approximately 10 percent), it is available for bonding parts together (i.e., the charge plate and diaphragm). In other words, the epoxy and its polymerization are “staged” in order to facilitate the overall process. Later, the epoxy is re-heated to reactivate polymerization and complete the curing cycle. 
         [0025]    In this way, and as compared with other approaches, the blending/depositing process (blending of resin and hardener, then depositing the liquid on a substrate) is separated from the curing process (after the liquid is deposited, immediately curing the liquid with time or heat) thereby adding flexibility to the manufacturing process. 
         [0026]    In one example of the operation of the system of  FIGS. 1 and 2 , sound energy enters through a sound port in a microphone assembly (not shown) and vibrates the diaphragm  104  and this action creates a corresponding change in electrical potential (voltage) between the diaphragm  104  and the charge plate  102 . In the absence of the sound energy, the diaphragm  104  is separated from the charge plate  102  by the constant or nearly constant distance d. The separation is secured using a stitch  108  to provide mechanical strength and to ensure that the distance is maintained. 
         [0027]    This voltage represents the sound energy that has been received. Typically, the voltage is then transmitted to an electric circuit ((e.g., an integrated circuit such as an application specific integrated circuit (ASIC)). Further processing of the signal may be performed on the electrical circuit. For instance, amplification or filtering functions may be performed on the voltage signal at the integrated circuit. 
         [0028]    Referring now to  FIG. 3 , another example of a stitch that is shaped differently from the example of  FIGS. 1 and 2  is described. The elements of  FIG. 3  are the same as those in  FIGS. 1 and 2  so that their descriptions are not repeated here.  FIG. 3  illustrates that stitches can take on a number of different shapes and dimensions. 
         [0029]    Referring now to  FIG. 4 , one example of a method for making an ECM microphone with a stitch is described. 
         [0030]    At step  402 , the b-stage epoxy/polyimide (e.g., Kapton) assembly is removed from frozen storage. The assembly is kept frozen prior to use to prolong its life by decelerating cure and to make it easier to handle, as it is not as tacky in the frozen or chilled state. At step  404 , the shape of the stitch is cut out which can be accomplished using a conventional die stamping process or by using a laser cutting process. 
         [0031]    At step  406 , the epoxy/polyimide (e.g., Kapton) stitch is put down over the charge plate and diaphragm ring, bridging the gap between them, and tacking their position. At step  408 , the epoxy/polyimide (e.g., Kapton) stitch and its adjacent components (charge plate and diaphragm ring) is put in an oven and heated (e.g., at 90 degrees Celsius) for approximately two hours whereas, the oven process renders the stitch attached to the diaphragm and the charge plate, and they are removed from the oven. 
         [0032]    In this example, the epoxy/polyimide film assembly functions as a mechanical support; however, it will be appreciated that the principles described herein can also be applied to other functions, such as creating an air tight seal around the perimeter of the microphone diaphragm. 
         [0033]    In this example, the device is a microphone; however, it will be appreciated that the principles described herein can also be applied to other types of devices, such as armature balanced receivers. 
         [0034]    Preferred embodiments of this invention are described herein, including the best mode known to the inventors for carrying out the invention. It should be understood that the illustrated embodiments are exemplary only, and should not be taken as limiting the scope of the invention.