Patent Publication Number: US-11647329-B2

Title: Microphone unit

Description:
TECHNICAL FIELD 
     The present invention relates to a microphone unit. 
     BACKGROUND ART 
     International Publication No. WO2015/056443 (hereinafter referred to as Patent Literature 1) discloses a microphone having a waterproof mechanism as a conventional example. 
     The microphone disclosed in Patent Literature 1 includes a diaphragm, a housing the inside of which is processed into a hemispherical surface, a parabolic curved surface or a conical surface, an acoustic transducer for converting sound pressure into an electric signal, and a wiring for transmitting the electric signal from the acoustic transducer to the outside. A sound pressure input surface of the acoustic transducer is arranged on a bottom surface part of the hemispherical surface, the parabolic curved surface, or the conical surface of the inside of the housing, and a waterproof mechanism for preventing infiltration of water is provided to the diaphragm and the housing, and also provided to the housing and the wiring. 
     Not so many conventional waterproof mechanisms have exhibited performance of withstanding a water resistance test of the highest level IPX9K (ISO20653, JISD5020) in an in-vehicle IP (K) test. Further, a method for implementing a microphone satisfying such performance requirements in a compact size and at low cost has not been known. 
     SUMMARY OF THE INVENTION 
     Therefore, an object of the present invention is to provide a compact and low-cost microphone unit that can conform to the highest level IPX9K of an in-vehicle IP (K) test. 
     A microphone unit according to the present invention comprises: a tubular case having an opened top and an opened bottom; a waterproof film made of metal that has a thickness of 0.01 mm or more and 0.05 mm or less, a hardness of 100 HV or more, a proof stress of 70 N/mm 2  or more, and a tensile strength of 350 N/mm 2  or more, the waterproof film being fixed to the bottom of the case so as to block an opening part of the bottom of the case; a substrate arranged in the case; a microphone mounted on the substrate; and a sealing member that seals an opening part of the top of the case. 
     Effects of the Invention 
     According to the present invention, it is possible to realize a compact and low-cost microphone unit that can comfort to the highest level IPX9K of the in-vehicle IP (K) test. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a plan view of microphone units of a first embodiment and a first modification; 
         FIG.  2    is a cross-sectional view of the microphone unit of the first embodiment based on a cutting line  2 - 2  and a projection direction indicated by arrows in  FIG.  1   ; 
         FIG.  3    is a bottom view of a substrate; and 
         FIG.  4    is a cross-sectional view of the microphone unit of the first modification based on the cutting line  2 - 2  and the projection direction indicated by the arrows in  FIG.  1   . 
     
    
    
     DETAILED DESCRIPTION 
     Hereinafter, an embodiment of the present invention will be described in detail. Components having the same functions are designated by the same reference numerals, and duplicate description thereof will be omitted. 
     First Embodiment 
     Hereinafter, the structure of a microphone unit of a first embodiment will be described with reference to  FIGS.  1  and  2   . As shown in  FIG.  2   , the microphone unit  1  of the present embodiment comprises a tubular case  11  having an opened top and an opened bottom, a waterproof film  12  made of metal which is fixed to the bottom of the case  11  so as to block an opening part of the bottom of the case  11 , a spacer  13  made of a conductive material which is pinched between the substrate  14  and the waterproof film  12 , a substrate  14  arranged in the case  11 , a microphone  15  mounted on the substrate  14 , and a sealing member  16  for sealing an opening part of the top of the case  11 . A hole  145  is formed in the substrate  14 , and a hole  165  is formed in the sealing member  16 . An amplifier circuit, a filter circuit, and an equalizer circuit are mounted on the substrate  14  as electronic circuits for adjusting characteristics. In the present embodiment, a MEMS microphone is assumed, but this can be replaced with an ECM or a dynamic microphone. When an ECM or dynamic microphone is used, the heat resisting temperature changes, so that it is necessary to pay attention to this point when designing. 
     For the case  11  is selected a material that can withstand a high water pressure (for example, 10 MPa), and is compatible with the material of a vibrating film. For example, a SUS case may be used. The thickness of the case  11  (t 1  in  FIG.  2   ) is suitably set to about 0.2 mm to 3.0 mm. 
     For the material of the waterproof film  12  is suitable a material that has no air permeability, has springiness, and returns to its original shape even when it is pressed and deformed, and a metal thin film that is not easily corroded, for example, a SUS film may be used, which improves water resistance and waterproofness. Similar performance can be achieved by using a thin film of resin as the waterproof film  12 . 
     Further, the waterproof film  12  is configured to have a thickness (t 2  in  FIG.  2   ) of 0.01 mm or more and 0.05 mm or less, a hardness of 100 HV or more, a proof stress of 70 N/mm 2  or more, and a tensile strength of 350 N/mm 2  or more, whereby it is possible to achieve a waterproof structure that meets the highest level of IPX9K in the in-vehicle IP (K) test. Elongation of 10% or more may be set as an additional condition. As a result, the microphone unit  1  of the present embodiment can be used as an external microphone because it can achieve a waterproof structure that can withstand high-pressure washing. 
     The waterproof film  12  may be fixed to the bottom of the case  11  by spot welding or seam welding. Further, the waterproof film  12  may be bonded to the bottom of the case  11  with an adhesive or a strong double-sided adhesive tape. By firmly bonding the waterproof film  12  and the case  11 , the bonded part will not be damaged even under high water pressure (for example, 10 MPa). 
     The distance between the substrate  14  and the waterproof film  12  is a parameter for adjusting the sensitivity, and the optimum value thereof also varies depending on the structure and the vibration diameter. For example, when the film thickness of the waterproof film  12  (SUS film) is set to 30 μm and the outer diameter thereof is set to ϕ14 (vibration diameter: ϕ12), the distance between the substrate  14  and the waterproof film  12  is suitably set to 0.01 mm to 0.5 mm. In the present embodiment, the height of the spacer  13  (t 3  in  FIG.  2   ) is set to 0.1 mm or more and 0.5 mm or less to provide a gap between the substrate  14  and the waterproof film  12 , whereby the distance between the substrate  14  and the waterproof film  12  is set to 0.1 mm or more and 0.5 mm or less. 
     Further, by adjusting the distance between the substrate  14  and the waterproof film  12 , the microphone unit is structured such that the substrate  14  supports the waterproof film  12  even under high water pressure (for example, 10 MPa), so that the limit of the proof stress of the waterproof film  12  is hardly exceeded and the restoration time of the waterproof film  12  can be shortened. 
     It is also possible to further miniaturize the microphone unit  1  by reducing the diameter of the microphone unit  1  and making the film thickness of the waterproof film  12  smaller. 
     When the substrate  14  and the case  11  are joined to each other, the substrate  14  and the case  11  may be joined to each other by pressing from above with a highly elastic adhesive or a structure such as a cap. It is possible to cope with atmospheric pressure fluctuation occurring at a temperature of 105° C. to −40° C. by the springiness of the waterproof film  12  and the fixing method of the substrate  14  (a method using a highly elastic adhesive). 
     As shown in  FIG.  3   , a GND pattern  147  is provided on the outer edge of the bottom surface of the substrate  14 , and the GND pattern  147  and the spacer  13  (conductive material) are brought into contact with (connected to) each other, whereby the case  11  and the waterproof film  12  can be used as a shield, so that resistance to static electricity and electromagnetic noise is improved. When the spacer  13  is made of a non-conductive material, it can be replaced by forming a GND pattern on the surface of the substrate  14  and connecting the GND pattern to the case  11  with a conductive material. 
     First Modification 
     As shown in  FIG.  4   , the waterproof film  12  may be fixed to the lower end of the case  11  by press-fitting the waterproof film  12  and a washer  17  into a groove  111  provided on the inner circumference of the lower end of the case  11  so that the waterproof film  12  and the washer  17  are fitted (clamped) to each other. The waterproof film  12  is fixed by spot welding or seam welding as in the case of the first embodiment, or the waterproof film  12  is clamped together with the washer  17  as in the case of the first modification, whereby the structure can withstand a pressure of 10 MPa and a water pressure under water. 
     &lt;Usage of the Microphone Units of the First Embodiment and the First Modification&gt; 
     The microphone units of the first embodiment and the first modification can be used for the following articles, for example. 
     1) Waterproof microphone, outdoor microphone, external microphone 
     2) Vending machine (voice recognition microphone) 
     3) Security camera 
     4) Entrance door (voice recognition microphone, intercom, etc.) 
     5) Vehicle backward warning buzzer control microphone 
     6) Keyless unlocking/locking answerback sound control microphone 
     7) Failure detection of heavy machinery and robots