Abstract:
A silicon condenser microphone has an additional back chamber and a sound hole in a PCB. The microphone includes a case for blocking an external sound; a substrate including a chamber case, a MEMS chip having an additional back chamber formed by the chamber case, an ASIC chip for operating the MEMS chip, a conductive pattern for a bonding to the case, and a sound hole for passing the external sound. A fixing means fixes the case to the substrate and an adhesive is applied to an entirety of a bonding surface of the case and the substrate fixed by the fixing means. When the sound hole is formed through the PCB instead of the case, the mounting space for a microphone is reduced. The chamber case forms the additional back chamber under the MEMS chip and is employed to increase back chamber space to improve sensitivity and reduce noise.

Description:
TECHNICAL FIELD 
     The present invention relates to a condenser microphone, and more particularly to a silicon condenser microphone having an additional back chamber and a sound hole in a PCB. 
     BACKGROUND ART 
     Generally, a condenser microphone widely used in a mobile communication terminal and an audio system comprises a voltage bias element, a pair of a diaphragm and backplate for constituting a capacitor C varying according to a sound pressure, and a JFET (Junction Field Effect Transistor) for buffering an output signal. The conventional condenser microphone is assembled by sequentially inserting a vibrating plate, a spacer ring, an insulation ring, a backplate and a conductive ring in a case, and finally inserting a PCB and curling an end portion of the case toward the PCB. 
     Recently, a semiconductor processing technique using micromachining is proposed as a technique for integrating a microscopic device. MEMS (Micro Electro Mechanical System) employs a semiconductor manufacturing process, an integrated circuit technology, in particular, to manufacture a microscopic sensor, an actuator and an electromechanical structure having a size in units of microns. In accordance with a MEMS chip microphone manufactured via the micromachining technology, conventional components of the microphone such as the vibrating plate, the spacer ring, the insulation ring, the backplate and the conductive ring may be miniaturized and integrated, and may have high performance, multi-function, high stability and a high reliability through a high precision microscopic process. 
       FIG. 1  is a diagram exemplifying a conventional MEMS chip structure used in a silicon condenser microphone. Referring to  FIG. 1 , a MEMS chip  10  has a structure wherein a backplate  13  is formed on a silicon wafer  14  using MEMS technology, and a vibrating plate  11  is disposed having a spacer  12  therebetween. The backplate  13  includes a sound hole  13   a  formed therein, and the MEMS chip  10  is generally manufactured by micromachining technology and a semiconductor chip manufacturing technology. 
       FIG. 2  is a lateral cross-sectional view illustrating a conventional silicon condenser microphone employing the MEMS chip. Referring to  FIG. 2 , a conventional silicon condenser microphone  1  is assembled by mounting the MEMS chip  10  and an ASIC (application specific integrated circuit) chip  20  on a PCB  40  and inserting the same in a case  30  having a sound hole  30   a  formed therein. 
     However, as shown in  FIG. 2 , because a back chamber  15  of the conventional silicon condenser microphone  1  is formed by the MEMS chip  10 , a space of the back chamber  15  is extremely small due to a size of the MEMS chip  10  which is a semiconductor chip. Therefore, a sound quality of the microphone is degraded. 
     SUMMARY 
     It is an object of the present invention to provide a silicon condenser microphone having an additional back chamber and a sound hole in a PCB in order to improve an acoustic characteristic. 
     In order to achieve the above-described object, there is provided a silicon condenser microphone comprising: a case for blocking an inflow of an external sound; a substrate including a chamber case, a MEMS chip having an additional back chamber formed by the chamber case, an ASIC chip for operating the MEMS chip, a conductive pattern for bonding to the case, and a sound hole for passing the external sound therethrough; a fixing means for fixing the case to the substrate; and an adhesive for a bonding the case and the substrate, wherein the adhesive is applied to an entirety of a bonding surface of the case and the substrate fixed by the fixing means. 
     As described above, the present invention includes a chamber case for forming an additional back chamber under a MEMS chip in order to increase a back chamber space of the MEMS chip, thereby improving sensitivity and noise problems such as a THD (Total Harmonic Distortion). 
     In addition, when a sound hole is formed in a substrate instead of a case, the microphone may be mounted on a main PCB via various methods. Therefore, a mounting space may be small. In addition, since the case is fixed to a PCB by a laser welding and bonded by an adhesive, the case is fixed during the bonding to prevent a generation of a defect, and a mechanical firmness is improved due to a high bonding strength. Thereby the silicon condenser microphone in accordance with the present invention is robust to external noise, and reduces a processing cost and the manufacturing cost. 
     While the present invention has been particularly shown and described with reference to the preferred embodiment thereof, it will be understood by those skilled in the art that various changes in form and details may be effected therein without departing from the spirit and scope of the invention. 
    
    
     
       DESCRIPTION OF DRAWINGS 
         FIG. 1  is a diagram exemplifying a conventional MEMS chip structure used in a silicon condenser microphone. 
         FIG. 2  is a lateral cross-sectional view illustrating a conventional silicon condenser microphone employing a MEMS chip. 
         FIG. 3  is a lateral cross-sectional view illustrating a silicon condenser microphone having an additional back chamber and a sound hole in a PCB in accordance with a first embodiment of the present invention. 
         FIG. 4  is a lateral cross-sectional view illustrating a silicon condenser microphone having an additional back chamber and a sound hole in a PCB in accordance with a second embodiment of the present invention. 
         FIG. 5  is a diagram exemplifying an additional back chamber in a form of a square pillar in accordance with the present invention. 
         FIG. 6  is a diagram exemplifying an additional back chamber in a form of a cylinder in accordance with the present invention. 
         FIG. 7  is a lateral cross-sectional view illustrating an example wherein a microphone having a connection terminal formed on a component surface is mounted on a main PCB in accordance with the first embodiment of the present invention. 
         FIG. 8  is a lateral cross-sectional view illustrating an example wherein a microphone is mounted on a main PCB in accordance with the second embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     The above-described objects and other objects and characteristics and advantages of the present invention will now be described in detail with reference to the accompanied drawings. 
       FIG. 3  is a lateral cross-sectional view illustrating a silicon condenser microphone having an additional back chamber and a sound hole in a PCB in accordance with a first embodiment of the present invention. 
     As shown in  FIG. 3 , the silicon condenser microphone  100  having an additional back chamber  152  and a sound hole  140   a  in accordance with the first embodiment has a structure wherein a chamber case  150  for forming the additional back chamber  152  and an ASIC chip  120  for driving an electrical signal of a MEMS chip  110  are disposed on a PCB substrate  140  having a conductive pattern  141  and connection terminals  142  and  144 , a MEMS chip  110  is disposed on the chamber case  150 , and a case  130  is attached to the PCB substrate  140 . The conductive pattern  141  and the ground connection terminal  144  are connected via a through-hole  146 . 
     The chamber case  150  increases a space of the back chamber of the MEMS chip  110  to improve sensitivity and improve noise problems such as THD (Total Harmonic Distortion), wherein a through-hole  150   a  for connecting a back chamber  15  formed by the MEMS chip  110  with the additional back chamber  152  is disposed on an upper surface of the chamber case  150 . The MEMS chip  110  has a structure wherein the backplate  13  is formed on the silicon wafer  14  using the MEMS technology and the vibrating plate  11  is formed to have the spacer  12  therebetween as shown in  FIG. 1 . The chamber case  150  may have a shape of a square pillar or a cylinder, and may be manufactured using a metal or a mold resin. In addition, although not shown, electrical wiring is disposed on the chamber case  150  so as to transmit the electrical signal of the MEMS chip  110  to the ASIC chip  120 . 
     The chamber case  150  having the through-hole  150   a  on an upper surface thereof for forming the additional back chamber, the MEMS chip  110  attached on the through-hole  150   a  of the chamber case  150  to expand the back chamber, and the ASIC chip  120  are disposed on the PCB substrate  140 . The conductive pattern  141  is disposed on a portion of the PCB substrate  140  that is in contact with the case  130 . The sound hole  140   a  for passing through an external sound is disposed at a position wherein the chamber case  150  is mounted, a sealing pad  148  for carrying out a hole sealing of the sound hole  140   a  by soldering for preventing a distortion of a sound wave in a space between a main PCB (reference numeral  310  in  FIG. 7 ) and the microphone is disposed around the sound hole  140   a  disposed at a lower surface of the PCB substrate  140 . A reference numeral  148   a  denotes a sound hole formed by the sealing pad  148 . 
     The case  130  is a metal case having one surface open wherein the case  130  has the shape of the cylinder or the square pillar. The case  130  has an end portion in contact with the conductive pattern  141  of the PCB substrate  140  and has a closed bottom surface to prevent an inflow of the external sound as well. The case  130  is attached to the PCB substrate  140  by aligning the metal case  130  on the conductive pattern  141  formed on the PCB substrate  140  and then spot-welding at least two points by a laser welding or a spot welding and then sealing a contacting portion of the case  130  and the PCB substrate  140  with an adhesive  164  such as an epoxy. A reference numeral  162  denotes a welding point. 
     In accordance with a method for manufacturing the silicon condenser microphone  100  of the first embodiment, after the chamber case  150  is mounted on the PCB substrate  140  such that the sound hole  140   a  of the PCB substrate  140  is positioned inside the additional back chamber  152  and the ASIC chip  120  is mounted on the PCB substrate  140 , the MEMS chip  110  is attached to the chamber case  150  such that the through-hole  150   a  of the chamber case  150  is positioned inside the back chamber  15  of the MEMS chip  110 . 
     Thereafter, the case  130  having the shape of the cylinder or the square pillar is fixed to the conductive pattern  141  of the PCB substrate  140  by the laser welding. The case  130  is bonded to the PCB substrate  140  by the adhesive  164 . The adhesive  164  may be a conductive epoxy, a non-conductive epoxy, a silver paste, a silicon, a urethane, an acryl and/or a cream solder. 
     Referring to  FIG. 3 , the MEMS chip  110  having the additional back chamber  152  formed by the chamber case  150  and the ASIC chip  120  are mounted on the PCB substrate  140 , and the square or circular conductive pattern  141  is disposed at a portion that is in contact with the case  130  having the shape of the cylinder or the square pillar. Since a size of the PCB substrate  140  is larger than that of the case  130  having the shape of the cylinder or the square pillar, a connection pad or the connection terminal for connecting to an external device may be freely disposed on the large PCB substrate, and the conductive pattern  141  may be manufactured by disposing a copper film via a conventional PCB manufacturing process and then plating a nickel or a gold. A ceramic substrate, a flexible PCB (FPCB) substrate or a metal PCB may be used instead of the PCB substrate  140 . 
     The case  130  having the shape of the cylinder or the square pillar has a contacting surface with the PCB substrate  140  open such that chip components may be housed inside, wherein an upper surface thereof is closed the external sound does not flows in. The case  130  may be manufactured using a brass, a copper, a stainless steel, an aluminum or a nickel alloy and may be plated with gold or silver. 
     After aligning the case  130  to the conductive pattern  141  of the PCB substrate  140 , a welding point  162  which is a portion of the contacting portion is welded with the laser using a laser welder (not shown) to fix the case  130  to the PCB substrate  140 . Thereafter, an assembly of the microphone is complete by applying the adhesive  164  to the entire contacting portion. The welding refers to spot-welding one or more points (preferably two or four points) in order to fix the case  130  to the PCB substrate  140  rather than welding an entire contacting surface of the case  130  and the PCB substrate  140 . A bonding point formed between the case  130  and the PCB substrate  140  through such welding is referred to as the welding point  162 . The case  130  is fixed to the PCB substrate  140  by the welding point  162  such that the case  130  is not moved during a bonding using the adhesive  164  or a curing process for bonding at a proper position. In addition, the conductive pattern  141  is connected to the ground connection terminal  144  through the through-hole  146 , and when the case  130  is bonded, external noise is blocked to remove the noise. 
     At least two and up to eight connection terminals  142  and  144  for connecting to the external device may be formed at a bottom surface of the PCB substrate  140 , and each of the connection terminals  142  and  144  is electrically connected to a chip component side through the through-hole. Particularly, in accordance with the embodiment of the present invention, when the connection terminals  142  and  144  extend about the PCB substrate  140 , the rework may be facilitated by using an electric solder through an exposed surface. 
     In accordance with the embodiments of the present invention, while the laser welding is exemplified as a method for fixing the case  130  to the PCB substrate  140 , a soldering or a punching may be used for fixing the case  130  to the PCB substrate  140 , and the conductive epoxy, the non-conductive epoxy, the silver paste, the silicon, the urethane, the acryl or the cream solder may be used as the adhesive  164 . 
       FIG. 4  is a lateral cross-sectional view illustrating a silicon condenser microphone having an additional back chamber and a sound hole in a PCB in accordance with a second embodiment of the present invention. A difference between the silicon condenser microphone  100  of the first embodiment and the silicon condenser microphone  100 ′ of the second embodiment is a position of the sound hole  140   a  formed in the PCB substrate  140 , wherein the sound hole  140   a  is formed at a position of the additional back chamber  152  formed by the chamber case  150  in case of the first embodiment and the sound hole  140   a  is formed between the chamber case  150  and the ASIC chip  120  away from the chamber case  150  in case of the second embodiment. 
     Therefore, while the silicon condenser microphone  100  of the first embodiment has a back type structure wherein the external sound passes through the sound hole  140   a  of the PCB substrate  140  to reach the additional back chamber  152 , the silicon condenser microphone  100 ′ of the second embodiment has a structure wherein the external sound passes through the sound hole  140   a  of the PCB substrate  140  and then passes through a space in the case  130  to reach the MEMS chip  110 . In accordance with the first embodiment, it is preferable that positions of the backplate  13  and the vibrating plate  11  are exchanged in a structure of the MEMS chip shown in  FIG. 1 . 
     In accordance with the silicon condenser microphone  100 ′ of the second embodiment, since a constitution thereof is identical to that of the silicon condenser microphone  100  of the first embodiment except the position of the sound hole  140   a , an additional detailed description is omitted. 
       FIG. 5  is a diagram exemplifying an additional back chamber in the form of the square pillar in accordance with the present invention, and  FIG. 6  is a diagram exemplifying an additional back chamber in the form of the cylinder in accordance with the present invention. 
     As shown in  FIGS. 5 and 6 , the chamber case  150  for forming the additional back chamber  152  may have the shape of the square pillar  150 ′ and the cylinder  150 ″, and the through-hole  150   a  is disposed on an upper portion of the square pillar  150 ′ or the cylinder  150 ″ to form a path with the back chamber  15  of the MEMS chip  110 . 
     The silicon condenser microphone  100  having various shapes may be manufactured by attaching the case  130  having various shapes on the PCB substrate  140 . The ASIC chip  120  and the MEMS chip  110  are mounted on the PCB substrate  140 . The MEMS chip  110  includes the additional back chamber  152  by the chamber case  150 . For instance, the case may have the shape of the cylinder, the square pillar, a cylinder having a wing at an end thereof, or a square pillar having a wing at an end thereof. 
       FIG. 7  is a lateral cross-sectional view illustrating an example wherein a microphone having a connection terminal formed on a component surface is mounted on a main PCB in accordance with the first embodiment of the present invention. 
     As shown in  FIG. 7 , in accordance with a silicon condenser microphone according to an alternate first embodiment, after the case  130  having the shape of the cylinder or the square pillar is fixed to the PCB substrate  140  larger than the case by welding, the case  130  is bonded by the adhesive  164 . The connection terminals  142  and  144  for connecting to a connection pad  320  of the main PCB  310  of a product on which the microphone is mounted are disposed in the component side of the PCB substrate  140 . At least two and up to eight connection terminals may be formed. The reference numeral  162  denotes the welding point. When the connection terminals extend to a sidewall of the substrate or extend to an opposite surface of the component side in addition to the sidewall, heat transfer of the electric solder is improved to facilitate the rework. 
     The main PCB  310  of the product on which the silicon condenser microphone is mounted comprises a circular or a square inserting hole  310   a  in order to mount the case  130  of the silicon condenser microphone. The connection pad  320  corresponding to the connection terminals  142  and  144  is disposed on the PCB substrate  140  of the microphone. 
     As shown in  FIG. 7 , in accordance with the silicon condenser microphone mounted on the main PCB  310 , the connection pad  320  of the main PCB  310  is coupled to the connection terminals  142  and  144  by soldering  330 . The case  130  extruding at a center of the component side of the substrate  140  is inserted the inserting hole  310   a  of the main PCB  310 . 
     Therefore, in accordance with a mounting method of the present invention, since the case  130  extruding over the PCB substrate of the microphone is inserted in the inserting hole  310   a  of the main PCB  310 , an overall height after the mounting is smaller than the conventional microphone wherein the connection terminals are formed on an opposite side of the component side to be mounted the main PCB, resulting in an efficient use of a space needed for mounting the product. 
       FIG. 8  is a lateral cross-sectional view illustrating an example wherein a microphone is mounted on a main PCB in accordance with the second embodiment of the present invention. 
     The silicon condenser microphone in accordance with the second embodiment of the present invention has a constitution identical to that of  FIG. 4 , and a main PCB  300  for mounting the silicon condenser microphone of the second embodiment comprises a sound hole  300   a  for passing through a sound form an external source, a sealing pad  302  disposed around the sound hole  300   a , and a connection pad  304  corresponding to the connection terminals  142  and  144  of the microphone as shown in  FIG. 8 . 
     Therefore, after aligning the sound hole  140   a  formed on the PCB substrate  140  of the silicon condenser microphone of the second embodiment to the sound hole  300   a  of the main PCB  300  and connecting terminals  142  and  144  to the connection pad  304 , the silicon condenser microphone is attached to the main PCB  300  via a soldering  330 . 
     The present invention includes a chamber case for forming an additional back chamber under a MEMS chip in order to increase a back chamber space of the MEMS chip, thereby improving sensitivity and noise problems such as a THD (Total Harmonic Distortion).