Abstract:
A condenser microphone with a novel structure has a stack of an electronic circuit board ( 16   a ), a backplate substrate ( 13   a ) having a backplate ( 14 ), a spacer ( 10   a ), and a diaphragm support frame ( 1   a ) supporting a diaphragm ( 2 ) so that the diaphragm faces the backplate across the spacer. The outer contours of the electronic circuit board, the backplate substrate and the spacer are the same in shape and size. The outer contour of the diaphragm support frame has portions coincident in shape and size with the outer contours of the electronic circuit board, the backplate substrate and the spacer and further has recesses formed on inward from the outer contours of the electronic circuit board, the backplate substrate and the spacer.

Description:
[0001]    This application claims priority under 35 U.S.C. §119 to Japanese Patent Application No. JP2006-024140 filed Feb. 1, 2006, the entire content of which is hereby incorporated by reference. 
       BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to a compact condenser microphone that is widely usable in portable electronic devices such as cellular phones and so forth, and also relates to a method of producing the condenser microphone. 
         [0004]    2. Description of the Related Arts 
         [0005]    Electret condenser microphones using an electret dielectric film (hereinafter referred to as simply “condenser microphones”) have heretofore been employed in a wide variety of fields because they are simple in structure, easy to miniaturize and low in cost. In recent years, the condenser microphones have been used as microphones of cellular phones, for which demand has been increasing rapidly. Accordingly, it is demanded that the condenser microphones should become smaller in size, higher in performance and lower in cost. 
         [0006]      FIG. 6(   a ) is a sectional view of a conventional condenser microphone  30 . As illustrated in the figure, the condenser microphone  30  has an electronic circuit board  32  having an electronic element, e.g. an FET  31 , mounted thereon. A backplate substrate  33 , a spacer  34  and a diaphragm support frame  36  are successively stacked on the electronic circuit board  32  and bonded together. The backplate substrate  33  has a backplate  33   a  on the upper side thereof and is provided on the lower side thereof with a recess for accommodating the FET  31 . The diaphragm support frame  36  has a diaphragm  35  stretched on the lower side thereof. 
         [0007]    The spacer  34  and the backplate substrate  33  are provided with vias (not shown), etc. to allow the diaphragm  35  and the backplate  33   a  to be electrically connected to the electronic circuit board  32 . 
         [0008]      FIG. 6(   b ) shows a stacked component assembly  40  as an intermediate product before the above-described condenser microphone is made as an end product. More specifically, the stacked component assembly  40  is formed by successively stacking an electronic circuit board assembly  41 , a backplate substrate assembly  42 , a spacer assembly  43 , and a diaphragm support frame assembly  44 . 
         [0009]    As shown in the figure, the diaphragm support frame assembly  44  is formed from a multiplicity of diaphragm support frames  36 , each having a quadrangular outer contour. The diaphragm support frames  36  are integrally arrayed in a lattice in contact with each other. The diaphragm support frame assembly  44  has a sheet as a diaphragm stretched over the entire area of the lower side thereof. In  FIG. 6(   b ), reference symbols  45   x  and  45   y  denote dividing lines between the mutually contacting diaphragm support frames  36 . Similarly, the electronic circuit board assembly  41  is formed from a multiplicity of quadrangular electronic circuit boards  32  having the same outer size as that of the diaphragm support frames  36 . The electronic circuit boards  32  are integrally arrayed in a lattice in contact with each other across dividing lines. The backplate substrate assembly  42  is formed from a multiplicity of quadrangular backplate substrates  33  having the same outer size as that of the diaphragm support frames  36 . The backplate substrates  33  are integrally arrayed in a lattice in contact with each other across dividing lines. The spacer assembly  43  is formed from a multiplicity of quadrangular spacers  34  having the same outer size as that of the diaphragm support frames  36 . The spacers  34  are integrally arrayed in a lattice in contact with each other across dividing lines. 
         [0010]    The above-described condenser microphone is produced as shown in  FIG. 7 . That is, the stacked component assembly  40  is mounted on a dicing sheet  50  in such a manner that the surface of the diaphragm support frame assembly  44  is fixed to the dicing sheet  50 . The stacked component assembly  40  set as stated above is cut by a dicing blade  51  in the stacking direction along the dividing lines  45   x  and  45   y.    
         [0011]    The above-described condenser microphone producing method can obtain a multiplicity of products at a time. Therefore, productivity increases, and cost reduction can be achieved. It is also possible to produce homogeneous components and hence easy to carry out quality control, which leads to an increase in yield. 
         [0012]    An invention relating to the above-described condenser microphone producing method is disclosed, for example, in Japanese Patent Application Publication No. 2002-345092. 
         [0013]    The conventional condenser microphone producing method suffers, however, from the following problems. 
         [0014]      FIG. 8  is an enlarged sectional view showing the way in which the stacked component assembly  40  is cut to prepare the above-described condenser microphone. In  FIG. 8 , when the dicing blade  51  cuts the stacked component assembly  40  along the dividing lines  45   x  and  45   y , the diaphragm support frame assembly  44 , which is located at the bottom of the stacked component assembly  40 , is pressed downward by shearing force applied by the dicing blade  51 , together with the diaphragm  35  attached to the diaphragm support frame assembly  44 . Consequently, the diaphragm support frame assembly  44  is likely to separate from the spacer assembly  43  near the dividing lines  45   x  and  45   y.    
         [0015]      FIG. 9  is a sectional view showing a condenser microphone in which the above-described separation has occurred. In such a condenser microphone  30 , external contaminant such as water or dust is likely to enter a slight gap between the diaphragm  35  and the backplate substrate  33  during use, causing degradation of the performance and reliability of the condenser microphone. 
         [0016]    Separation due to cutting is likely to occur particularly when a thin metal sheet such as a stainless steel sheet is used as a material constituting the diaphragm support frame assembly  44  to reduce the thickness and cost of the condenser microphone. When a stainless steel or other metal sheet is used as the material of the diaphragm support frame assembly  44 , frictional heat is generated by friction between the dicing blade  51  and the diaphragm support frame assembly  44 , which is a metal sheet, and the heat discharges the electric charge implanted in the electret layer on the backplate  33   a  formed on the backplate substrate assembly  42 . Consequently, the sensitivity of the microphone lowers, and the performance thereof degrades. 
       SUMMARY OF THE INVENTION 
       [0017]    Accordingly, an object of the present invention is to provide a condenser microphone capable of solving the above-described problems, and also provide a method of producing the condenser microphone. 
         [0018]    That is, the present invention provides a condenser microphone including an electronic circuit board, a backplate substrate having a backplate, a spacer, and a diaphragm support frame supporting a diaphragm so that the diaphragm faces the backplate, wherein the electronic circuit board, the backplate substrate, the spacer and the diaphragm support frame are successively stacked. The outer contours of the electronic circuit board, the backplate substrate and the spacer are the same in shape and size. The outer contour of the diaphragm support frame has portions coincident in shape and size with the outer contours of the electronic circuit board, the backplate substrate and the spacer and further has recesses positioned inside the outer contours of the electronic circuit board, the backplate substrate and the spacer. 
         [0019]    Namely, in the condenser microphone according to the present invention, the outer contour of the diaphragm support frame has recesses as stated above. Therefore, even if the condenser microphone is formed from the above-described stacked component assembly by performing dicing with a dicing blade along the outer contour (dividing lines), the recessed portions of the diaphragm support frame will not contact the dicing blade. Accordingly, the recessed portions of the diaphragm support frame will not be pressed downward by shearing force of the dicing blade. Thus, it is possible to avoid the problem of separation of the diaphragm support frame from the spacer assembly. 
         [0020]    Specifically, the arrangement may be as follows. The outer contours of the electronic circuit board, the backplate substrate and the spacer are quadrangular. The outer contour of the diaphragm support frame has four sides corresponding to the outer contours of the electronic circuit board, the backplate substrate and the spacer, and a predetermined number of recesses as stated above are formed along respective the four sides. 
         [0021]    More specifically, the recesses may include four elongated recesses formed on respective said four sides each of which extends from a center of corresponding one of the four sides to near both ends of the corresponding one. 
         [0022]    The diaphragm support frame may be made of a metal material such as a stainless steel. 
         [0023]    In addition, the present invention provides a condenser microphone producing method including the steps of providing an electronic circuit board assembly having a multiplicity of quadrangular electronic circuit boards integrally arrayed in a lattice in contact with each other, and preparing a backplate substrate assembly having a multiplicity of quadrangular backplate substrates integrally arrayed in a lattice in contact with each other. Each of the backplate substrates has a backplate and has the same outer size as that of the electronic circuit boards. The method further includes the steps of preparing a spacer assembly having a multiplicity of quadrangular spacers integrally arrayed in a lattice in contact with each other, the spacers having the same outer size as that of the electronic circuit boards, and providing a diaphragm support frame assembly having a multiplicity of diaphragm support frames integrally arrayed in a lattice in contact with each other. The diaphragm support frame assembly has a diaphragm stretched over the entire area of one side thereof. Each of the diaphragm support frames has a quadrangular outer contour. The outer contour has portions coincident with the outer size of the electronic circuit board and has recesses positioned inside the outer contour of the electronic circuit board. The electronic circuit board assembly, the backplate substrate assembly, the spacer assembly and the diaphragm support frame assembly are successively stacked and bonded together in such a manner that dividing lines between the mutually contacting electronic circuit boards of the electronic circuit board assembly, dividing lines between the mutually contacting backplate substrates of the backplate substrate assembly, dividing lines between the mutually contacting spacers of the spacer assembly and dividing lines between the mutually contacting diaphragm support frames of the diaphragm support frame assembly align with each other in the stacking direction, thereby fabricating a stacked component assembly. The stacked component assembly is cut in the stacking direction along the dividing lines aligned with each other, thereby preparing a multiplicity of condenser microphones each having a stack of the quadrangular electronic circuit board, the quadrangular backplate substrate having a backplate, the quadrangular spacer, and the diaphragm support frame supporting a diaphragm so that the diaphragm faces the backplate. 
         [0024]    According to the condenser microphone producing method of the present invention, each diaphragm support frame constituting the diaphragm support frame assembly has recesses along the outer contour thereof. Therefore, even if the stacked component assembly is cut as stated above, the recessed portions of the diaphragm support frame will not be pressed downward by shearing force of the dicing blade  51 . Accordingly, it is possible to avoid the problem of separation of the diaphragm support frame from the spacer assembly. 
         [0025]    Specifically, the condenser microphone producing method may further include the steps of preparing a dicing sheet, mounting the stacked component assembly on the dicing sheet in such a manner that an exposed side surface of the diaphragm support frame assembly of the stacked component assembly is fixed to the dicing sheet, and cutting the stacked component assembly mounted on the dicing sheet with a dicing blade set to extend in the stacking direction on the dividing lines by forcing the dicing blade through the stacked component assembly toward the dicing sheet in the stacking direction. 
         [0026]    The above and other objects, features and advantages of the present invention will become more apparent from the following description of the preferred embodiments thereof, taken in conjunction with the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0027]      FIG. 1  is an exploded perspective view of a stacked component assembly prepared as an intermediate product for making a condenser microphone according to the present invention. 
           [0028]      FIG. 2  is a top plan view showing a part of a diaphragm support frame assembly forming the topmost layer of the intermediate product shown in  FIG. 1 . 
           [0029]      FIG. 3(   a ) is a perspective view of the stacked component assembly shown in  FIG. 1 . 
           [0030]      FIG. 3(   b ) is a perspective view of the condenser microphone according to the present invention formed by cutting the stacked component assembly shown in  FIG. 3(   a ). 
           [0031]      FIG. 4  is a fragmentary sectional view of a part of the stacked component assembly, showing the relationship between a dicing blade and the stacked component assembly when the stacked component assembly is cut with the dicing blade. 
           [0032]      FIG. 5(   a ) is a perspective view of a condenser microphone according to an embodiment of the present invention. 
           [0033]      FIG. 5(   b ) is a sectional view of the condenser microphone shown in  FIG. 5(   a ). 
           [0034]      FIG. 6(   a ) is a sectional view of a conventional condenser microphone. 
           [0035]      FIG. 6(   b ) is a perspective view of a stacked component assembly for making the conventional condenser microphone. 
           [0036]      FIG. 7  is a fragmentary sectional view of a part of the conventional stacked component assembly, showing the relationship between the stacked component assembly and a dicing blade. 
           [0037]      FIG. 8  is a sectional view similar to  FIG. 7 , showing in an enlarged view the way in which the stacked component assembly is cut with the dicing blade. 
           [0038]      FIG. 9  is a sectional view showing problems associated with the conventional condenser microphone. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0039]    Embodiments of the present invention will be described below with reference to  FIGS. 1 to 5(   b ). 
         [0040]    A condenser microphone  22  according to an embodiment of the present invention has, as shown in  FIGS. 5(   a ) and  5 ( b ), an electronic circuit board  16   a , a backplate substrate  13   a , a spacer  10   a , and a diaphragm support frame  1   a , which are successively stacked, substantially in the same way as the above-described prior art. The diaphragm support frame  1   a  supports a diaphragm  2  planarly. The diaphragm  2  is supported so as to be exposed in a sound collecting hole  3  provided in the diaphragm support frame  1   a , as seen in a top plan view. 
         [0041]      FIG. 1  is an exploded perspective view of a stacked component assembly [denoted by reference numeral  21  in  FIGS. 3(   a ),  3 ( b ) and  4 ] prepared as an intermediate product for making the condenser microphone  22  as an end product. 
         [0042]    That is, the stacked component assembly  21  is formed by successively stacking and bonding together a diaphragm support frame assembly  1  having diaphragm support frames  1   a  integrally arrayed in a lattice, a spacer assembly  10  having spacers  10   a  integrally arrayed in a lattice, a backplate substrate assembly  13  having backplate substrates  13   a  integrally arrayed in a lattice, and an electronic circuit board assembly  16  having electronic circuit boards  16   a  integrally arrayed in a lattice. 
         [0043]    The diaphragm support frame assembly  1  is made of a sheet-shaped metal material such as a stainless steel (hereinafter abbreviated as “SS”). More specifically, the diaphragm support frame assembly  1  has a multiplicity of diaphragm support frames  1   a  integrally arrayed in a lattice. A sheet is stretched on the lower side of the diaphragm support frame assembly  1  as a diaphragm assembly having a multiplicity of diaphragms  2  integrally arrayed in a lattice in correspondence to the diaphragm support frames  1   a . Each diaphragm support frame  1   a  has a circular sound collecting hole  3  formed in the center thereof and small holes  4  formed at four corners of four sides defining the outer peripheral edge of the diaphragm support frame  1   a . Each diaphragm support frame  1   a  further has slots  5  formed along the four sides thereof. The slots  5  are preferably formed collectively by etching process or the like. The constituent material of the diaphragm support frame assembly  1  is not necessarily limited to SS but may be aluminum, brass, nickel silver, etc. 
         [0044]    Each spacer  10   a  of the spacer assembly  10  has a circular opening  11  provided in the center thereof and small holes  12  provided at four corners thereof. 
         [0045]    Each backplate substrate  13   a  of the backplate substrate assembly  13  has a circular electrically conductive backplate  14  provided on the upper side thereof and small holes  15  provided at four corners thereof. 
         [0046]    Each electronic circuit board  16   a  of the electronic circuit board assembly  16  has electronic elements, i.e. an FET  17   a  and chip condensers  17   b  and  17   c , provided on the upper side thereof, and further has small holes  18  provided at four corners thereof. Further, the electronic circuit board  16   a  has formed thereon electrode patterns (not shown) for electrically connecting the FET  17   a  and the chip condensers  17   b  and  17   c  and for electrical connection with the backplate substrate  13   a.    
         [0047]    The diaphragm support frame assembly  1 , the spacer assembly  10 , the backplate substrate assembly  13  and the electronic circuit board assembly  16  are successively stacked and bonded together in such a manner that the dividing lines of these assemblies align with each other in the stacking direction, i.e. the dividing lines between the mutually contacting electronic circuit boards of the electronic circuit board assembly  16 ; the dividing lines between the mutually contacting backplate substrates of the backplate substrate assembly  13 ; the dividing lines between the mutually contacting spacers of the spacer assembly  10 ; and the dividing lines  20   x  and  20   y  between the mutually contacting diaphragm support frames of the diaphragm support frame assembly  1 . The bonding may be carried out by using an adhesive or an adhesive sheet. If an adhesive sheet is used, one that has a configuration similar to that of the spacer assembly  10  shown in  FIG. 1  should preferably be used. 
         [0048]    The stacked component assembly  21  formed as stated above is mounted on a dicing sheet  23  in such a manner that the diaphragm support frame assembly  1  is fixed to the dicing sheet  23 , and then cut with a dicing blade  24  into small pieces constituting individual condenser microphones  20 . More specifically, the dicing blade  24  is set to extend in the stacking direction on the above-described dividing lines and then forced through the stacked component assembly  21  toward the dicing sheet  23 , thereby cutting the stacked component assembly  21 . 
         [0049]    The diaphragm support frame assembly  1  is provided with the slots  5  along the dividing lines  20   x  and  20   y , as has been stated above. The slots  5  are provided to minimize the shearing force of the dicing blade  24  applied to the diaphragm support frame  1   a  when the above-described cutting is performed with the dicing blade  24 . Preferably, the width of the slots  5  is set somewhat wider than the thickness of the dicing blade  24 . By doing so, it is possible to minimize the force applied to the diaphragm support frame  1   a  from the dicing blade  24  during cutting. Consequently, it is possible to avoid the problem that the diaphragm support frame assembly  1  is pressed downward, together with the diaphragm  2 , by the dicing blade  24 , so that the respective portions of the diaphragm support frame assembly  1  and the diaphragm  2  near the dividing line  20   y  separate from the spacer assembly  10  and the backplate substrate assembly  13 , as in the conventional art shown in  FIG. 8 . 
         [0050]    In the illustrated example, both ends of each of the slots  5  of the diaphragm support frame assembly  1 , which are formed along the dividing lines  20   x  and  20   y , are at a distance A from the respective outer peripheries of the small holes  4  close to them, as shown in  FIG. 2 . The distance A is preferably about 0.3 mm for an embodiment. 
         [0051]    Although the slots  5  in this embodiment are rectangular, it should be noted that the configuration of the slots  5  is not necessarily limited thereto but may be altered at will without departing from the gist of the present invention. 
         [0052]      FIGS. 5(   a ) and  5 ( b ) show a condenser microphone  22  made from the intermediate product (i.e. stacked component assembly)  21 . The condenser microphone  22  comprises a stack of a diaphragm support frame  1   a , a spacer  10   a , a backplate substrate  13   a  and an electronic circuit board  16   a , which are arranged in the mentioned order from top to bottom. The condenser microphone  22  has recesses extending in the stacking direction on four corners thereof that are formed as a result of cutting the vertically superimposed small holes  4 ,  12 ,  15  and  18  to a quarter of their original size. The recesses extending in the stacking direction can be used as vias for electrically connecting the stacked diaphragm support frame  1   a  and backplate substrate  13   a  to the electronic circuit board  16   a . The diaphragm support frame  1   a  has horizontally elongated recesses  5   a  on the four sides defining the outer periphery thereof, which are formed as a result of halving the slots  5 . 
         [0053]    The electronic circuit board  16   a  has electronic elements such as an FET  17   a  and chip condensers  17   b  and  17   c  mounted thereon in the same way as in the above-described conventional art. The backplate substrate  13   a  is provided at the lower side thereof on the electronic circuit board  16   a  with a recess  13   b  for accommodating the FET  17   a  and so forth. The backplate substrate  13   a  has a circular backplate  14  formed on the upper side thereof. The backplate  14  has an electret layer (not shown) formed on the upper side thereof from an electret dielectric film. 
         [0054]    In this structure, the diaphragm  2  and the backplate  14  on the backplate electrode substrate  13   a  face each other across a slight gap to function as a capacitor. When external sound passing through the sound collecting hole  3  causes the diaphragm  2  to vibrate, the capacitance of the capacitor formed by the diaphragm  2  and the backplate  14  slightly changes. The change in capacitance is converted into an electric signal by the FET  17   a , and the electric signal is output to the outside. Thus, the device functions as a microphone. 
         [0055]    As will be understood from the above, the condenser microphone according to the present invention features that when the diaphragm support frame assembly  1  is cut with the dicing blade  24  during the manufacture of the condenser microphone, only the portions extending over the distance A, which are shown in  FIG. 2 , are subjected to cutting. Accordingly, it is possible to prevent the diaphragm support frame assembly  1  separating from the spacer assembly  10  by shearing force applied from the dicing blade  24  in the cutting step and also suppress the generation of heat due to friction between the dicing blade  24  and the diaphragm support frame assembly  1 . Thus, it is possible to minimize the above-described problems associated with the conventional condenser microphone. 
         [0056]    In addition, because the diaphragm support frame assembly  1  is formed from a metal material such as SS, the required strength can be ensured satisfactorily even if it is thin. Therefore, it is possible to realize a reduction in thickness of the condenser microphone. Because SS and other similar material are low in cost, the condenser microphone can be reduced in cost. Although SS used as a material of the diaphragm support frame assembly  1  has a high rigidity, wear of the dicing blade  24  is minimized because the diaphragm support frame assembly  1  is formed with the slots  5 . Accordingly, the dicing blade  24  can have an extended lifetime, and the production cost can be further reduced. 
         [0057]    It should be noted that the present invention is not necessarily limited to condenser microphones but may be readily applied to other articles manufactured by integrating a multiplicity of components to fabricate an assembly as an intermediate product and then cutting it to prepare an end product, and also applied to production methods for such articles. Although the stacked component assembly  21  in the embodiment of the present invention has a total of 9 condenser microphones  22  integrally arrayed in a lattice, the number of condenser microphones  22  is not necessarily limited to 9. In actual practice, a stacked component assembly having several hundreds of condenser microphones can be used in the manufacturing process. 
         [0058]    It should be noted that the present invention is not necessarily limited to the foregoing embodiments but can be modified in a variety of ways without departing from the gist of the present invention.