Abstract:
A microphone ( 100 ) and method of manufacture thereof is disclosed. The microphone ( 100 ) includes a housing ( 108 ), a diaphragm assembly ( 120 ), a spacer ( 134 ), a backplate assembly ( 140 ), a body assembly ( 150 ), and a printed circuit board ( 164 ) disposed within the housing ( 100 ). The diaphragm assembly ( 120 ) and the backplate assembly ( 140 ) constitute a variable capacitor responsive to sound pressure level changes coupled through an acoustic port ( 118 ). The base capacitance is inversely proportional to the thickness of the spacer ( 134 ). The backplate assembly ( 140 ) is disk shaped with protrusions and coupled to the body assembly ( 150 ) such that an acoustic passage ( 172 ) is formed between an outer edge of the backplate assembly ( 140 ) and an inner periphery of the hollow body assembly ( 150 ). The body assembly ( 150 ) comprises conductive mount ( 158 ) for electrically coupling the backplate assembly ( 140 ) to a first surface ( 166 ) of a circuit board ( 164 ). A second surface ( 168 ) of the circuit board ( 164 ) is then held in contact with the connecting surface ( 114 ) of the housing ( 108 ) by mechanical fastening such as crimping, soldering, welding or adhesive bonding.

Description:
CROSS REFERENCE 
     This application is a division of U.S. application Ser. No. 10/801,371, filed Mar. 16, 2004, the disclosure of which is hereby incorporated herein by reference in its entirety for all purposes. 
    
    
     TECHNICAL FIELD 
     This patent relates to microphones and more particularly to high performance electret microphones used in communication devices, audio devices or the like, and a method of manufacturing the same. 
     BACKGROUND 
     Mobile communication technology has progressed rapidly in recent years. Consumers are increasingly using mobile communication devices such as cellular phones, web-enabled cellular telephones, Personal Digital Assistants (PDAs), hand-held computers, laptops, tablets and other devices capable of communication over public or private communication networks. The expansion of cellular networks and technological advancements in mobile communications have resulted in more consumers using mobile communications devices. This increased demand for communication devices drives improvements in the manufacturing processes, power consumption, reception, fabrication, and miniaturization of audio components incorporated in the mobile communication devices. Competitive pressures among suppliers of mobile communication devices increase the demand for smaller, less expensive, and better performing miniature capacitor microphones. 
     Generally speaking, a variety of conventional electret condenser microphones (“ECMs”) have been used for communication devices. A prior art ECM comprises a dust guard, a housing with an acoustic port, a vibratory diaphragm, a spacer, an insulating body, a backplate assembly, a conductive ring, and a printed circuit board (“PCB”). The diaphragm assembly and the backplate assembly constitute a variable capacitor portion responsive to sound pressure level changes coupled through the acoustic port corresponding to the thickness of the spacer. 
     As the size of the ECM is reduced, limited space is available to accommodate the insulating body and the conductive ring resulting in increased interference between the capacitor portion and the PCB. Apart from the pursuit of miniaturization repetitive shocks and vibration may create a deleterious effect on acoustic performance of ECMs over time. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an exploded view of a capacitor microphone; 
         FIG. 2  is a top view of a backplate assembly; 
         FIG. 3  is a top view of a body assembly; 
         FIG. 4  is a perspective view showing the configuration of the backplate and the body assembly; 
         FIG. 5  is a top view of  FIG. 4  of the configuration of the backplate and the body assembly; and 
         FIG. 6  is a cross-sectional view of a capacitor microphone. 
     
    
    
     DETAILED DESCRIPTION 
     While this invention is susceptible to various modifications and alternative forms, certain embodiments are shown by way of example in the drawings and these embodiments will be described in detail herein. It should be understood, however, that this disclosure is not intended to limit the invention to the particular forms described, but to the contrary, the invention is intended to cover all modifications, alternatives, and equivalents falling within the spirit and scope of the invention defined by the appended claims. 
       FIG. 1  is an exploded view of a capacitor microphone  100  that can be used in virtually any type of communication device such as cellular phones, web-enabled cellular telephones, Personal Digital Assistants (PDAs), hand-held computers, other types of portable computing and Internet access appliances and devices, and the like, capable of communication over one or more public or private communication networks. The microphone  100  may include a cup-shaped housing  108  having an upper surface portion  110  and a side wall portion  112 . In alternate embodiments, the housing  108  may take the form of various other shapes (e.g. rectangular, D-shaped, or trapezoid-shaped) and have a number of different sizes. The side wall portion  112  of the housing terminates at a connecting surface  114 , defining an opening  116 . The connecting surface  114  may be initially formed with an outward flare to enable placement of the other components in the housing  108 . 
     When all the components are placed in final or closed position within the housing  108 , the connecting surface  114  is bent or re-formed radially toward the center of the opening  116 . This forming operation mechanically captures the back surface  168  of the PCB  164  by the connecting surface  114 , locking the other components in position as well as electrically connecting the back surface  168  of the PCB  164 . The housing  108  is shown to have at least one layer. However, the housing  108  may be fabricated from alternating layers of conductive materials and non-conductive materials or a non-conductive substrate may have a conductive coating applied on the inside allowing electrical connection of the diaphragm assembly  120  to the back surface  168  of the PCB  164 . In one embodiment, the housing  108  is made of aluminum. 
     At least one aperture or acoustic port  118  is introduced on the upper surface  110  of the housing  108  to allow acoustic waves to be transmitted to the diaphragm assembly  120 . The acoustic port  118  may be formed in any suitable manner such as drilling, punching or molding. The acoustic port  118  allows acoustic energy corresponding to sound pressure level changes to enter the housing  108 . 
     A dust guard  102  in the form of a shape corresponding to the shape of the housing  108 , but may take the form of various shapes not necessarily corresponding to the housing shape, and may have a number of different sizes. In one embodiment, the dust guard  102  is shown to have a circular shape corresponding to the circular shape of the housing  108 . The dust guard may be made of cloth or felt having a first surface  104  and a second surface  106 . The second surface  106  of the dust guard  102  is attached to the housing  108  by adhesive to cover the acoustic port  118 . This helps to prevent debris from entering the microphone  100  damaging the electronic components  170  disposed within the housing  108 . The dust guard  102  may also improve the frequency response, create delay and provide directional response. 
     The microphone  100  may further include a diaphragm assembly  120 . The diaphragm assembly  120  includes a support ring  122  and a diaphragm  124  attached to the support ring  122 . The diaphragm assembly  120  has a shape that generally corresponds to that of the housing  108  but may take the fort of various shapes and have a number of different of sizes in different embodiments. The support ring  122  may be made of electrically conductive material such as stainless steel; however, any conductive material or material including a conductive coating, including brass or tin may be utilized. The support ring  122  has a first surface  126  and a second surface  128 . The first surface  126  of the support ring  122  is held in contact with the upper surface  110  and the second surface  128  is held in contact with a spacer  134 . The diaphragm  124  is made of an electrically conductive material capable of vibrating in response to acoustic waves. One such material is a polyethylene terephthalate film, commonly available under the trademark Mylar. The diaphragm  124  has a first surface  130  and a second surface  132 . The first surface  130  of the diaphragm  124  is attached to the second surface  128  of the support ring  122 , for example, by bonding with adhesive. However, it will be understood by those or ordinary skill in the art that any form of joining would suffice, including compression, or mechanical attachment at the edges, and the like. The second surface  132  of the diaphragm  124  is coated with a layer of conductive material such as chromium forming an electrically active portion, commonly referred to as the movable electrode is held in contact with a spacer  134 . 
     The microphone  100  may further include a spacer  134  having a hollow section  135  and first and second surfaces,  136  and  138  respectively, for electrically isolating the diaphragm assembly  120  from other components within the housing  108 . The spacer  134  is made of an electrically insulating material such as a 200 gauge Mylar plastic having a thickness spaced between the diaphragm assembly  120  and a backplate assembly  140 . The spacer  134  enables deflection of the diaphragm  124  toward the backplate assembly  140 . The spacer  134  may have various shapes not necessarily corresponding to the housing shape and may have a number of different sizes. In one embodiment, the spacer  134  is shown to have a circular in shape corresponding to the housing  108 . The spacer  134  thickness and materials may vary depending on the requirements of the application. The spacer  134  is placed between the diaphragm assembly  120  and the backplate assembly  140  and held in place by mechanical pressure exerted by the connecting surface  114  after it is closed over the PCB  164 . The first surface  136  of the spacer  134  is held in contact with the second surface  132  of the diaphragm  124 . The second surface  138  of the spacer  134  is held in contact with the backplate assembly  140  and separates the diaphragm assembly  120  from the backplate assembly  140 . 
     The microphone  100  may further include a backplate assembly  140 . The backplate assembly  140  is shown to have at least one protrusion  142  and at least one relief section  144 . However, the backplate assembly may include a plurality of protrusions  142   a - d  and a plurality of relief portions  144   a - d , and such embodiment will be discussed in greater detail. The backplate assembly  140  is held between the second surface  138  of the spacer  134  and the body assembly  150  by the mechanical pressure of the connecting surface  114  as discussed above. 
     The microphone  100  also has a body assembly  150  having a hollow section  152  and upper and lower surfaces  154  and  156 , respectively. The body assembly  150  is disposed within the housing  108 . The body assembly  150  may be molded in various shapes and sizes to suit the needs of the application. In one embodiment, the body assembly  150  is cylindrical in shape and is made of an electrically insulating material such as a molded polyethylene plastic. When assembled, the first surface  154  of the body assembly  150  is held in contact with the second surface  138  of the spacer  134  by the mechanical pressure of the connecting surface, as described above. The second surface  156  of the body assembly  150  is formed with a positioning projection member  160 . The positioning projection member  160  is designed to receive the PCB  164  to mechanically isolate, but electrically connect, the backplate assembly  140  to the PCB  164 . As such, the spacing between the backplate assembly  140  and the diaphragm assembly  120  are not affected by deformations in the housing  108 . In one example, the positioning projection member  160  is made of an electrically conducting material such as stainless steel; however, any conductive material or material including a conductive coating may be utilized. 
     The microphone  100  still further includes a printed circuit board (PCB)  164  disposed in the housing  108 . The PCB  164  may be coaxially aligned with the housing  108 . The PCB  164  has a front surface  166  and a back surface  168 . The PCB  164  may be formed in various shapes and sizes corresponding to the housing or otherwise according to specific applications. The front surface  166  of the PCB  164  may have printed wiring traces and a plurality of electronic components  170 , such as a junction field effect transistor (JFET) and at least one capacitor for converting the changes in electrical capacitance generated by the diaphragm assembly  120  and the backplate assembly  140  into electric impedance. The front surface  166  of the PCB  164  is held in contact with the positioning projection member  160  and electrically connected via the conductive mount  158  to the backplate assembly  140 . The back surface  168  has printed wiring traces and is electrically coupled to the housing  108  via the connecting surface  114 . The PCB  164  may be attached to the conductive mount  158  via a soldering process; however, any form of electrical connection would suffice. 
     The body assembly  150  is then press-fit into the housing  108  in contact with the spacer  134 . The press-fit of the body assembly  150  restrains the underlying components to reduce shifting and damage that may occur during manufacturing. Further, the body assembly  150  makes it possible that the backplate assembly  140  and the diaphragm assembly  120  are electrically connected with the PCB  170  with no deformation of the positioning projection member  160 . 
     Referring to  FIG. 2 , one embodiment of the backplate assembly  140  is shown. The backplate assembly  140  is punched into a disk shape having at least one protrusion  142  and at least one relief section  144 . In the embodiment shown, the backplate assembly  140  includes a plurality of protrusions  142   a - d  and a plurality of relief portions  144   a - d . The backplate assembly  140  is made of an electrically conducting material such as stainless steel; however, any conductive material or material including a conductive coating may be utilized. The backplate assembly  140  has a first surface  146  and a second surface  148 . The first surface  146  of the backplate assembly  140  may be coated or covered with a polarized dielectric film or electret material such as Teflon. In operation, the backplate forms a fixed electrode and may be electrostatically charged to a predetermined surface charge, for example, 360V. The second surface  148  is made of an electrically conducting material such as a stainless steel. Formed in this manner, the backplate assembly  140  has the advantage of increased surface area under the center, or most mobile areas of the diaphragm  124 , thereby increasing the electro-acoustic performance of the microphone  100 . A device built in accordance with the inventive concepts disclosed herein has the advantage of reduced overall size while maintaining good electro-acoustic performance for sensitivity, noise, stability, compactness, robustness, and insensitivity to electromagnetic interference (“EMI”) and other external and environmental conditions, including shock and debris. 
     Referring now to  FIG. 3 , the body assembly  150  is pressed or molded, in one embodiment, into a cylindrical shape, having the hollow section  152 . The body assembly  150  is made of an electrically insulating material such as molded polyethylene plastic having an upper surface  154  and a lower surface  156 . The positioning projection member  160  is made of an electrically conducting material such as stainless steel and may molded or press-fit into the lower surface  156  of the body assembly  150 . The upper ends  158   a - d  may be punched out and attached to or molded into the inner peripheral portion of the body assembly  150 . The conductive mount  158  and the positioning projection member  160  may be formed from the same stock and molded or press-fit to the body assembly  150  as one unit. Using a body assembly  150  provides the advantage of reduced overall size of the device while maintaining good electro-acoustic performance. In another embodiment the backplate assembly  140  may be round without protrusions  142   a - d . To create the necessary acoustic passages  172  the body assembly may be formed to provide a relief around at least a portion of the outer edge of the backplate assembly  140 . 
     Referring to  FIGS. 4 and 5 , the body assembly  150  and the backplate assembly  140  are discussed and described. The inner peripheral portion of the body assembly  150  is formed with a conductive mount  158  with a plurality of upper ends  158   a ,  158   b ,  158   c ,  158   d . In one example, the conductive mount  158  is made of an electrically conducting material such as stainless steel; however, any conductive material or material including a conductive coating may be utilized. The conductive mount  158  is electrically connected to the positioning projection member  160  by welding or soldering. The conductive mount  158  and the positioning projection member  160  may alternatively be formed from the same piece of stock. The conductive mount  158  is disposed to receive the second surface  148  of the backplate assembly  140 . Each protrusion  142   a - d  on the backplate assembly  140  is attached to a corresponding mounting point formed by the upper ends  158   a - d  of the conductive mount  158 . The attachment may be made by bonding with adhesive. Alternative forms of joining may include compression, mechanical attachment, and the like. The backplate assembly  140  may be joined to the body assembly  150  prior to mounting in the housing  108 , or the backplate assembly  140  may be joined to the body assembly  150  during final assembly of the microphone  100 . 
     The backplate assembly  140  is press-fit into the body assembly  150  and attached to the conductive mount  158  by bonding with adhesive disposed within the inner peripheral portion of the body assembly  150 . The alternating protrusions define a plurality of acoustic passages  172 . The acoustic passages  172  are located away from the high mobility center of the diaphragm to the outer edge of the backplate at the relief portions  144   a - d , allowing free flow of air in the space between the diaphragm  124  and the backplate assembly  140  to the back volume where the PCB  160  is situated without sacrificing performance. 
       FIG. 6  is a cross-sectional view that will be referred to in conjunction with a description of an embodiment of a method of assembling the microphone  100 . First, the diaphragm assembly  120  is inserted in the housing  108 , opposed to the acoustic port  118 . The spacer  134  is then inserted in the housing  108  with the first surface  136  of the spacer  134  facing the second surface  132  of the diaphragm assembly  120 . Next, the backplate assembly  140  is inserted into the body assembly  150 . The first surface  146  of the backplate assembly  140  is oriented to be facing the second surface  138  of the spacer  134  when inserted into the housing  108 . The plurality of protrusions  142   a - d  are aligned and adhered to the plurality of upper ends  158   a - d  of the conductive mount  158 . The body assembly  150  is then inserted into the housing  108 . The backplate assembly  140 , the spacer  134 , and the diaphragm assembly  120  are restrained from shifting their position due to vibrations occurring during manufacturing by the friction fit of the body assembly  150 . The second surface  156  of the body assembly  150  is formed with a positioning projection member  160  disposed at a position corresponding to the PCB  164 . The PCB  164  is preassembled with a plurality of electronic components  170 . After the diaphragm assembly  120 , the spacer  134 , the backplate assembly  140 , and the body assembly  150  are completely inserted into the housing  108 , the back surface  168  of the PCB  164  is captured by the connecting surface  114  of the housing  108  by mechanical fastening, crimping, welding or adhesive bonding, for instance. In this position, the diaphragm assembly  140  and the backplate assembly  140  are electrically connected with the PCB  164 . 
     All references, including publications, patent applications, and patents, cited herein are hereby incorporated by reference to the same extend as if each reference were individually and specifically indicated to be incorporated by reference and were set forth in its entirety herein. 
     The use of the terms “a” and “an” and “the” and similar referents in the context of describing the invention (especially in the context of the following claims) are to be construed to cover both the singular and the plural, unless otherwise indicated herein or clearly contradicted by context. Recitation of ranges of values herein are merely intended to serve as a shorthand method of referring individually to each separate value falling within the range, unless otherwise indicated herein, and each separate value is incorporated into the specification as if it were individually recited herein. All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of any and all examples, or exemplary language (e.g., “such as”) provided herein, is intended merely to better illuminate the invention and does not pose a limitation on the scope of the invention unless otherwise claimed. No language in the specification should be construed as indicating any non-claimed element as essential to the practice of the invention. 
     Several 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.