Abstract:
A package structure of a micro-electromechanical system (MEMS) type microphone is disclosed. The MEMS microphone comprises a substrate, a MEMS chip, an acoustic wave cover, and an encapsulant. The substrate has connection pads. The MEMS chip is electrically coupled to the connection pads. The MEMS chip includes an acoustic wave sensing portion. The acoustic wave cover is fixed on the MEMS chip for covering without contacting the acoustic wave sensing portion and defining an acoustic wave cavity space. The acoustic wave cover has an opening for allowing an acoustic wave to enter or exit out of the acoustic cavity space. The encapsulant encapsulates the substrate, the MEMS chip, and the acoustic wave cover, wherein a surface of the acoustic wave cover is exposed. The exposed surface of the acoustic wave cover is along the same level as the surface of the encapsulant.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
   This application claims the priority benefit of Taiwan application serial no. 95131712, filed Aug. 29, 2006. All disclosure of the Taiwan application is incorporated herein by reference. 
   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a package structure and a packaging method of a micro-electromechanical (MEMS) microphone. 
   2. Description of Related Art 
   Under the influence of the popular global communication, it is common that one person may have one or more mobile phones or everyone has a mobile phone. Even students carry mobile phones to school for communicating with parents, and thus the mobile phone consumer age is significantly lowered to below 10-year old. 
   Further, the Topology Research Institute points out in the September 2005 research report that the global shipment quantity of the mobile phones in 2005 was about 760 million, and the number of mobile phone users may reach up to 1.685 billion. The Topology also predicts that the global mobile phone users may be up to 2.236 billion. Therefore, the market scale of mobile phone application cannot be ignored. 
   Along with the increasing demands for video and audio functions, currently, in mobile phones worldwide, a new microphone, in addition to the microphone used for talking, is provided for the capturing video images, so as to provide convenience in service use. Therefore, the demand for the microphone grows increasingly. 
   The MEMS microphone has a thin thickness and small volume. Furthermore, the surface adhering process can be performed by solder reflow to effectively reduce the assembly cost. Therefore, in order to meet the requirements of the mobile phone with small volume and low cost, the MEMS microphone applied to gradually replace the original electric condenser microphone (ECM) on the market. 
   Moreover, the MEMS microphone has an innate advantage of low power consumption (160 μA) that is ⅓ of that of ECM. When applied in the mobile phones with limited power storage, this power saving advantage promotes the MEMS microphone to replace the ECM. 
   For other products equipped with microphone, the demands for the MEMS microphone tend to grow. For example, currently, the MEMS microphone is increasingly applied in electronic products such as portable walkman and digital camera for micro hard disks and flash memories. Therefore, in the future, it is possible for the MEMS microphone to have a considerable market in the electrical application fields. 
   For the current MEMS microphone, referring to  FIG. 1 , a sectional view of the current Knowles MEMS microphone module structure is shown. 
   A MEMS microphone chip  10  and a logic chip  20  are electrically coupled to a base plate  30 . By using a conductive glue  32 , a support ring  40  and a top plate  50  are successively stacked on the base plate  30 , so as to constitute one acoustic wave cavity space V 1  (referring to  FIG. 2 ). The MEMS microphone chip  10  has an acoustic wave sensing portion  12 , and the top plate  50  has an opening  52  for allowing the acoustic wave to enter or exit out of the acoustic wave cavity space V 1  to be sensed by the acoustic wave sensing portion  12 . In the acoustic wave cavity space V 1 , a liquid compound  34  is sealed on the logic chip  20  by using a dispensing process, so as to protect the logic chip  20  and the contacts to the base plate  30 . The liquid compound  34  cannot be dispensed onto the MEMS microphone chip  10  since once being dispensed on the MEMS microphone chip  10 , the liquid compound  34  may flow onto the acoustic wave sensing portion  12 , further affecting the performance of the MEMS microphone module. 
   Referring to  FIG. 3 , a sectional view of the MEMS microphone module structure disclosed in the U.S. Pat. No. 6,781,231 B2 according to another conventional art is shown. 
   A conductive housing  120  having a sound-hole  144  in the middle thereof is adopted. The housing  120  can be integrated as a whole or a combination structure of constructed by stacking through two stages. The housing  120  is used to protect the MEMS microphone chip  110  and the logic element  112  therebeneath. The conductive housing  120  and all the elements under the conductive housing  120  are not filled with any material in between. That is, all the space under the conducting housing  120  can be used as the acoustic wave transmitting space (the volume V 2  of acoustic wave cavity, referring to  FIG. 4 ). 
   As far as the module assembly is concerned, the sealed bonding of the integrally fabricated conductive housing  120  and the substrate  114  therebeneath is achieved by using an adhesive and a solder for one monomer at a single time. The two-stage stacked conductive housings  125   a ,  125   b  are successively selected and placed one by one and bonded by two stages. Moreover, for the solder wire of electrical interconnection in the package, the monomer dispensing method is used to dispense the liquid epoxy resin individually in the area assembled with the solder wire, and then a heating hardening process is performed to cure the epoxy resin, so as to achieve the purpose of protecting the solder wire. 
   Similarly, based on the above reasons, the dispensing protection cannot be used for the MEMS microphone chip. 
   Also, in the current technique, the MEMS microphone chip is disposed in the acoustic wave cavity space, and is not protected by the molding compound, thus resulting in the following disadvantages. 
   (1) If the MEMS microphone module falls onto the ground (for example the mobile phone drops onto the ground), because the solder wire contacts of the MEMS microphone chip is not protected by the molding compound and may get damaged, and the reliability of the microphone is adversely affected. 
   (2) The external damp easily enters from the opening (sound-hole), and affects contacts to the substrate, so that the reliability of the module is reduced. 
   SUMMARY OF THE INVENTION 
   Accordingly, the present invention is directed to a package structure of a MEMS microphone, which comprises a substrate having a connection pad; a MEMS microphone module electrically coupled to the connection pad of the substrate, and having an acoustic wave sensing portion; an acoustic wave cover, fixed on the MEMS microphone chip, and covering without touching the acoustic wave sensing portion, so as to define an acoustic wave cavity space, in which the acoustic wave cover has an opening for the acoustic wave go in or go out the acoustic wave cavity space; and an encapsulant, encapsulating the substrate, the MEMS microphone module, and the acoustic wave cover, and exposing a surface of the acoustic wave cover, wherein the exposed surface of the acoustic wave cover is even with the surface of the encapsulant. 
   The encapsulant encapsulating the substrate and the MEMS microphone protects the MEMS microphone chip and contacts, thereby alleviating the influence of the external vibration and the environmental damp. According to an embodiment of the present invention, the acoustic wave cavity is reserved for transmitting the acoustic wave. 
   According to the defined acoustic wave cavity comprises a smaller space than the conventional art, and therefore the restraining frequency is improved to obtain a broader sensing range of the acoustic wave. 
   Additionally, the encapsulant is used to replace the conventional top plate and support ring structure, and thus the volume of the module is greatly reduced and the relative processes of coating conductive glue between the layers can be avoided. The encapsulant may be used to replace the full cover housing structure, and the volume of the module can be greatly reduced. 
   The present invention is also directed to a method of packaging the MEMS microphone, which comprises the following steps. A wafer having a plurality of MEMS microphone chips is provided, wherein each of the MEMS microphone chips comprises an acoustic wave sensing portion. At least an acoustic wave cover is provided. The acoustic wave cover is bonded onto the wafer, so as to make the acoustic wave cover being fixed on the MEMS microphone chips to cover without touching the acoustic wave sensing portion. The wafer is sawed to separate the MEMS microphone chips and obtain a plurality of module units, wherein each of the module units comprises a MEMS microphone chip and an acoustic wave cover fixed on the MEMS microphone chip. A substrate having a plurality of module areas is provided, wherein each of the module area has a connection pad. The module units are electrically coupled to the connection pads of the module areas of the substrate. An encapsulant is formed with a molding compound material to encapsulate the substrate and the module units, and to expose a surface of the acoustic wave cover and make the surface of the encapsulant being even with the surface of the acoustic wave cover. And, a singulation step is performed to cut the encapsulant and the substrate according to the module areas, so as to obtain a plurality of package structures of MEMS microphone. 
   According to an embodiment of the present invention, a plurality of acoustic wave covers is fixed onto a plurality of MEMS microphone chips in a single step, and each component can be processed at the same time, thus the step of individually assembling the single housings may be avoided and thereby effectively increase the throughput. 
   According to an embodiment of the present invention, a mature molding process such as resin transfer molding can be used to package and protect a whole batch of MEMS microphone chips and the contacts in a single step, thereby saving the time for dispensing as in the case of the conventional art. Also, the process technique is mature, and thereby achieve a high production yield, high throughput, and reduce the manufacturing cost. 
   In the above MEMS microphone package structure, the MEMS microphone chip is a system chip which is formed by integrating the MEMS microphone chip and logic chip as a whole. Due to this characteristic, the package volume can be further reduced. 
   In order to the make aforementioned and other objects, features and advantages of the present invention comprehensible, a preferred embodiment accompanied with figures are described in detail below. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a sectional view of a conventional Knowles MEMS microphone module structure. 
       FIG. 2  shows an acoustic wave cavity of the MEMS microphone module structure of  FIG. 1 . 
       FIG. 3  is sectional view of another conventional MEMS microphone module structure. 
       FIG. 4  shows an acoustic wave cavity of the MEMS microphone module structure of  FIG. 3 . 
       FIGS. 5-14  show a method of packaging the MEMS microphone according to a first embodiment of the present invention. 
       FIG. 15  shows a package structure of the MEMS microphone according to a second embodiment of the present invention. 
       FIG. 16  shows a package structure of the MEMS microphone according to a third embodiment of the present invention. 
       FIG. 17  is a schematic plan view of a wafer. 
       FIG. 18  is an isometric view of  FIG. 10 . 
       FIG. 19  shows an acoustic wave cavity in the MEMS microphone package structure according to the first embodiment of the present invention. 
   

   DESCRIPTION OF EMBODIMENTS 
   The First Embodiment 
   Referring to  FIGS. 5-14 , a method of packaging the MEMS microphone according to the first embodiment of the present invention is described. 
   Referring to  FIGS. 5 and 17 ,  FIG. 17  is a schematic plan view of the wafer, and  FIG. 5  is a side sectional view of  FIG. 17 . 
   A wafer  200  is provided. The surface of the wafer  200  comprises a plurality of MEMS microphone chips  202 . Each of the MEMS microphone chips  202  comprises at least a bonding pad  203 , as shown in  FIG. 5 . One bonding pad  203  and an acoustic wave sensing portion  202   a  for sensing the acoustic wave is shown for each MEMS microphone chip  202  for the purpose of illustration. 
   Referring to  FIG. 7 , at least one acoustic wave cover  212  is provided, and the material of the acoustic wave cover  212  comprises but not limited to a conductive material, an ordinary radio-frequency-interference shielding material, an electromagnetic interference shielding material, or the like. The acoustic wave cover  212  comprises at least an opening  213 . 
   The acoustic wave cover  212  is bonded onto the wafer  200 , and can be bonded by performing, for example, adhering or soldering, such that each acoustic wave cover  212  is fixed on each MEMS microphone chip  202 . The acoustic wave cover  212  covers without contacting the acoustic wave sensing portion  202   a , so as to define an acoustic wave cavity space V 3  (as shown in  FIG. 19 ) The shape of the cavity is not limited as in  FIG. 19 . The opening  213  of the acoustic wave cover  212  is provided for the acoustic wave to enter or exit out of the acoustic wave cavity space V 3 . 
   The method of bonding the acoustic wave cover  212  onto the MEMS microphone chip  202  is not limited herein, as long as the acoustic wave cover  212  can be fixed on the MEMS microphone chip  202  without departing from the scope of the present invention. For example, the wafer  200  can be heated, and the acoustic wave cover  212  is then pressed onto the wafer  200  to bond the two. Alternatively, when the acoustic wave cover  212  is bonded onto the wafer  200 , it is acceptable to bond one acoustic wave cover  212  or a plurality of acoustic wave covers  212  in a single step. 
   Next, referring to  FIG. 8 , the wafer  200  is sawed to separate the MEMS microphone chips  202  and to obtain a plurality of module units  220  (as shown in  FIG. 9 ). Each of the module units  220  includes a MEMS microphone chip  202  and an acoustic wave cover  212  fixed on the MEMS microphone chip  202 . 
   Referring to  FIGS. 10 and 18 ,  FIG. 10  is a schematic plan view of the substrate, and  FIG. 18  is an isometric view of  FIG. 10 . 
   A substrate  230  is provided. The substrate  230  is used to carry the electronic elements and the connection elements described below. For example, the substrate  230  can be a plastic substrate, a ceramic substrate, or even a flexible substrate (Flexible Print Circuitry). In this embodiment, the substrate  230  is comprised of, for example, a PCB (printed circuit board) having a plurality of module areas  230   a  and one or more connection pads  231  used for electrically coupling to the electronic elements described below. However, it should be noted that the substrate  230  is not limited to a PCB, and can be any equivalent structure capable of carrying and electrically coupling the electrical elements. 
   Referring to  FIG. 11 , a logic chip  204  is provided. Each logic chip  204  has at least a bonding pad  233 . Only one bonding pad  233  is shown on each logic chip  204  for illustration. The module units  220  and the logic chips  204  are electrically coupled to the connection pads  231  of the module areas  230   a  of the substrate  230 . Particularly, as an example of the above electrical coupling method, the bonding pad  203  of the MEMS microphone chip  202  is directly electrically coupled to the connection pad  231  of the substrate  230 , and the bonding pad  233  of the logic chip  204  is directly electrically coupled to the connection pad  230  of the substrate  230 , as shown in  FIG. 11 . However,  FIG. 11  is only an example, and is not intended to limit the scope of the present invention. The step of electrically coupling the MEMS microphone chip  202  of the module unit  220  to the connection pad  231  of the substrate  230  can also be achieved by the following method. The bonding pad  203  of the MEMS microphone chip  202  is first electrically coupled (e.g. wired) to the bonding pad  233  of the logic chip  204 , and then the bonding pad  233  of the logic chip  204  is electrically coupled (e.g. wired) to the connection pad  231  of the substrate (the examples of the coupling manner are not shown in the drawings of the first embodiment, but one of the examples is shown in  FIG. 15  of the second embodiment below). 
   Referring to  FIG. 12 , a molding compound material is used to form the encapsulant  240  which encapsulates the substrate  230 , the module unit  220 , and the logic chip  204 , exposes the surface  212   a  of the acoustic wave cover  212  and uses the predetermined shape of the mould to make the surface  240   a  of the encapsulant  240  being even with the surface  212   a  of the acoustic wave cover  212 . The molding compound material is a material commonly used in the packaging process, for example, it can be a resin material such as epoxy resin. 
   Referring to  FIG. 13 , a singulation step is performed for sawing and separating the encapsulant  240  and the substrate  230  according to the module areas  230   a , so as to obtain a plurality of MEMS microphone package structures  250  (as shown in  FIG. 14 ). 
   In this embodiment, although the MEMS microphone chip and the logic chip are encapsulated together in an encapsulant, however the present invention is not limited there-to, the logic chip can also be disposed outside the encapsulant. 
   According to an embodiment of the present invention, the MEMS microphone chip and the contacts are protected so as to alleviate the influence of the external vibration and the environmental damp. According to an embodiment of the present invention, the acoustic wave cavity can be reserved for transmitting the acoustic wave. 
   According to the Helmholtz resonance principle, the restraining frequency f e  may be expressed by the following formula: 
   
     
       
         
           
             
               
                 
                   f 
                   e 
                 
                 = 
                 
                   
                     c 
                     
                       2 
                       ⁢ 
                       π 
                     
                   
                   ⁢ 
                   
                     
                       s 
                       
                         Vl 
                         e 
                       
                     
                   
                 
               
             
             
               
                 ( 
                 
                   Formula 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   1 
                 
                 ) 
               
             
           
         
       
     
   
   In formula 1, V represents the volume of the acoustic wave cavity. That is, the volume of the acoustic wave cavity is smaller, and the restraining frequency f e  is higher. 
   According to an embodiment of the present invention, the defined acoustic wave cavity space is smaller than that of the conventional art (the conventional acoustic wave cavity is V 1  of  FIG. 2  and V 2  of  FIG. 4 , and the acoustic wave cavity of the present invention is V 3  of  FIG. 19 . It is obvious that V 3  is smaller than V 1  and is also smaller than V 2 ). Therefore, the restraining frequency f e  can be improved to expand the sensing range of the acoustic wave. 
   The encapsulant is used to replace the top plate and support ring structure of the conventional MEMS microphone module, so that the related process of coating conductive glue between the layers can be avoided so that the thickness of the module is reduced and the area of bonding pad can be reduced. Thus, the volume of the MEMS microphone module may be significantly reduced. Alternatively, the encapsulant is used to replace the full cover housing structure of the conventional MEMS microphone module so that the volume of the MEMS microphone module can be significantly reduced. According to the specification of the popular products worldwide, the thickness of the current Knowles MEMS microphone module is about 1.65 mm, and the area of the bonding pad is about 6.2*3.8 mm. However, the thickness of the package structure of the embodiment of the present invention can be up to 1.4 mm, and the area of the bonding pad is about 4.8*2.7 mm. Accordingly, the volume of the MEMS microphone module can be reduced to about 48% of that of the conventional MEMS microphone module. 
   By bonding the wafer having a plurality of MEMS microphone chips with a plurality of acoustic wave covers, a plurality of acoustic wave covers can be fixed on a plurality of MEMS microphone chips at the same time, and each component can be processed at the same time so that the process of individually assembling the single housing at each discrete step may be effectively avoided. That is, according to the present invention, thousands of acoustic wave covers and MEMS acoustic wave sensing chips can be bonded simultaneously in one process step before going through the sawing process, thus the production throughput can be greatly increased. 
   According to an embodiment of the present invention, a mature molding process such as resin transfer molding process can be used to package and protect a whole batch of MEMS microphone chips and the contacts at the same time so that the time for individually dispensing as in the conventional art may be effectively reduced. Also, because the process technique is mature, and therefore production throughput and yield, increasing the throughput, and reducing the manufacturing cost. 
   In the MEMS microphone package structure described above, the MEMS microphone chip can also be a system chip formed by integrating the MEMS microphone chip and the logic chip as a whole. Thus, the package volume can be further reduced. 
   The Second Embodiment 
   In the first embodiment, the MEMS microphone chip  202  and the logic chip  204  are disposed at the different positions of the substrate  230 , for example, disposed parallel on the substrate  230 . Referring to  FIG. 15 , in the second embodiment of the present invention, the MEMS microphone chip  202  is stacked on the logic chip  204 . For example, the module unit  220  is stacked on the logic chip after the module unit  220  is obtained. In this embodiment, the electrical coupling of the MEMS microphone chip  202  and the substrate  230  is achieved by electrically coupling the bonding pad  203  of the MEMS microphone chip  202  to the bonding pad  233  of the logic chip  204 , and then the connection pad  231  of the substrate is electrically coupled via the bonding pad  233  of the logic chip  204 . 
   The Third Embodiment 
   In the second embodiment, the MEMS microphone chip  202  is stacked on the logic chip  204 . Referring to  FIG. 16 , in the third embodiment of the present invention, the system chip  302  formed by integrating the MEMS microphone chip and the logic chip as whole can be adopted to replace the above stacking structure. The bonding pad  303  of the system chip  302  is directly wire-bonded to the connection pad  231  of the substrate. 
   It will be apparent to those skilled in the art that various modifications and variations can be made to the structure of the present invention without departing from the scope or spirit of the invention. In view of the foregoing, it is intended that the present invention cover modifications and variations of this invention provided they fall within the scope of the following claims and their equivalents.