Patent Publication Number: US-2012032282-A1

Title: Microelectromechanical system (mems) carrier and method of fabricating the same

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to carriers and methods of fabricating the same, and, more particularly, to a microelectromechanical system (MEMS) carrier and a method of fabricating the same. 
     2. Description of Related Art 
     Nowadays, MEMS devices such as microphones have been broadly used in the mobile communication equipment, audio message device, etc. In order to protect an MEMS device, a cover component is disposed thereon to prevent the MEMS device from being exposed and damaged. 
     Referring to  FIGS. 1A through 1E , cross-sectional diagrams depicting a method of disposing a cover component  1  on an MEMS device according to the prior art are shown. 
     As shown in  FIG. 1A , a core board  10  is provided that has at least a through hole  100  formed through the core board  10 , and an adhering layer  12  is formed on a surface of the core board  10 . 
     As shown in  FIG. 1B , a carrier layer  13  is adhered to the adhering layer  12 , and covers an end of the through hole  100 . 
     As shown in  FIG. 1C , a conductive seed-layer  14  is formed on the core board  10 , a sidewall of the through hole  100 , and the carrier layer  13  in the through hole  100 , and a shielding metal layer  15  is then formed on the conductive seed-layer  14  in an electroplating process. 
     As shown in  FIG. 1D , an acoustic hole  130  is formed through the carrier layer  13 , the conductive seed-layer  14 , and the shielding metal layer  15 , and a surface treatment layer  16  is formed on the shielding metal layer  15 . The cover component  1  is thus completed. 
     As shown in  FIG. 1E , a circuit board  11  has wire bonding pads  110 , and a microelectromechanical system (MEMS) component  31  and an application specific integrated chip (ASIC)  32  are disposed on the circuit board  11 . The MEMS component  31  is electrically connected to the ASIC  32  and the wire bonding pad  110  via conducive wires  33 . The cover component  1  is mounted on the circuit board  11  to cover the MEMS component  31  and the ASIC  32 . 
     According to the prior art, since the cover component  1  has the shielding metal layer  15  only, without any other functional metal layer, the cover component  1  can provide nothing but a function of covering the MEMS component  31  and the ASIC  32 . Consequently, both the MEMS component  31  and the ASIC  32  have to be mounted on the circuit board  11 , in order to be covered by the cover component  1 . Accordingly, the overall structure has an increased height, which is disadvantageous in miniaturization of electronic products. 
     Furthermore, since the MEMS component  31  has to be disposed on the circuit board  11 , a space S is thus required between the acoustic hole  130  of the cover component  1  and the MEMS  31 . As a result, the path of signal received by the MEMS component  31  is prolonged, and the signal stability and transmission speed are reduced. 
     Hence, how to overcome the drawbacks of the prior art is becoming one of the critical issues in the art. 
     SUMMARY OF THE INVENTION 
     In view of the drawbacks of the prior art mentioned above, it is therefore an objective of this invention to provide an MEMS carrier and a method of fabricating the same that is advantageous in miniaturization of electronic product. 
     To achieve the aforementioned and other objectives, the present invention provides an MEMS carrier, comprising: a core board having a first surface and an opposite second surface, a circuit layer formed on the first surface and having a plurality of conductive pads, and a through hole formed through the first and the second surfaces; a carrier layer formed on the second surface of the core board and covering an end of the through hole; a patterned metal layer formed on a portion of the carrier layer that covers the end of the through hole; a solder mask layer formed on the first surface of the core board and the circuit layer, and having a plurality of openings for exposing the conductive pads; and a shielding metal layer formed in the through hole for covering the patterned metal layer and the portion of the carrier layer that covers the end of the through hole. 
     The present invention further provides a method of fabricating an MEMS carrier, comprising the stages of: providing a core board having a first surface and an opposite second surface, and a circuit layer formed on the first surface; forming in the core board a through hole passing through the first and the second surfaces; forming on the second surface of the core board a carrier layer that covers an end of the through hole; formin a patterned metal layer on the carrier layer in the through hole; forming a solder mask layer on the first surface of the core board and the circuit layer; forming a plurality of openings in the solder mask layer for exposing a portion of the circuit layer, for the exposed portion of the circuit layer to serve as conductive pads; and forming a shielding metal layer in the through hole for covering the patterned metal layer and the portion of the carrier layer that covers the end of the through hole. 
     In an embodiment of the present invention, the shielding metal layer is formed by the following steps of: forming a conductive seed-layer on the solder mask layer, the conductive pads, the sidewall of the through hole, the patterned metal layer, and the portion of the carrier layer that covers the end of the through hole; forming a resist layer on the conductive seed-layer; forming an open area in the resist layer for exposing the conductive seed-layer on the sidewalls of the through hole, the patterned metal layer, and the portion of the carrier layer that covers the end of the through hole; forming the shielding metal layer on the exposed conductive seed-layer; and removing the resist layer and the conductive seed-layer covered thereby. 
     In an embodiment of the present invention, the conductive pads comprise wire bonding pads and ball planting pads. 
     In an embodiment of the present invention, the method further comprises forming on the second surface of the core board an adhering layer for adhering the carrier layer to the second surface of the core board via the adhering layer. 
     In an embodiment of the present invention, the carrier layer further comprises a bonding metal layer for attaching the carrier layer to the second surface of the core board via the bonding metal layer, and the bonding metal layer extends to a surface of the portion of the carrier layer that covers the end of the through hole. 
     In an embodiment of the present invention, the method further comprises forming a surface treatment layer on the conductive pads and the shielding metal layer, and the surface treatment layer is formed by using freedom chemical plating nickel/gold, Electroless Nickel Immersion Gold (ENIG), Electroless Nickel Electroless Palladium Immersion Gold (ENEPIG), Immersion Tin, or Organic Solderability Preservative (OSP). 
     Accordingly, the MEMS carrier of the present invention and method of fabricating the same, through the formation of the patterned metal layer on the carrier layer, an MEMS and ASIC are allowed to be mounted on the patterned metal layer and the carrier layer. As compared with the prior art, there is no need in the present invention to use a circuit board. Therefore, the overall structure has a reduced height, and is more advantageous in the miniaturization of electronic products. 
     Furthermore, since the MEMS is allocated on the patterned metal layer, the acoustic hole is thus located under the MEMS. As a result, a path of signal received by the MEMS is shortened, and the signal stability and transmission speed are enhanced. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       The invention can be more fully understood by reading the following detailed description of the preferred embodiments, with reference made to the accompanying drawings, wherein: 
         FIGS. 1A through 1E  are cross-sectional diagrams depicting a method of disposing a cover component on an MEMS device according to the prior art; 
         FIGS. 2A through 2I  are cross-sectional diagram depicting an MEMS carrier and a method of fabricating the same according to the present invention; 
       FIGS.  2 D′ and  2 D″ are two different embodiments of  FIG. 2D ; 
       FIG.  2 E′ is a top view of  FIG. 2E , and FIG.  2 E″ is another embodiment of FIG.  2 E′; 
       FIGS.  2 I′ and  2 I″ are two different embodiments of  FIG. 2I ; and 
         FIGS. 3 ,  3 ′ and  3 ″ are cross-sectional diagrams depicting different embodiments of mounting an MEMS and semiconductor component on the MEMS carrier according to the present invention. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     The following illustrative embodiments are provided to illustrate the disclosure of the present invention; those in the art can apparently understand these and other advantages and effects after reading the disclosure of this specification. The present invention can also be performed or applied by other different embodiments. The details of the specification may be on the basis of different points and applications, and numerous modifications and variations can be devised without departing from the spirit of the present invention. 
     Referring now to  FIGS. 2A through 2I , a method of fabricating an MEMS carrier according to the present invention is illustrated. 
     As shown in  FIG. 2A , a core board  20  is provided that has a first surface  20   a  and an opposite second surface  20   b,  and a circuit layer  21  is formed on the first surface  20   a.    
     As shown in  FIG. 2B , an adhering layer  22  is formed on the second surface  20   b  of the core board  20 . 
     As shown in  FIG. 2C , on the core board  20  and the adhering layer  22  at least one through hole  200  is formed that passes through the adhering layer  22 , the first surface  20   a,  and the second surface  20   b.    
     As shown in  FIG. 2D , a carrier layer  23  is bonded onto the second surface  20   b  of the core board  20  via the adhering layer  22 , and the carrier layer  23  covers an end of the through hole  200 . Moreover, a patterned metal layer  231  is formed on a portion of the carrier layer  23  that covers the end of the through hole  200 . 
     As shown in FIG.  2 D′, at the same time of forming the patterned metal layer  231  on the carrier layer  23 , a bonding metal layer  232  is formed for attaching the carrier layer  23  to the second surface  20   b  of the core board  20  via the adhering layer  22 . 
     In another embodiment, the bonding metal layer  232 ′ can extend to a surface of the portion of the carrier layer  23  that covers the end of the through hole  200 , and a different patterned metal layer  231 ″ is formed, as shown in FIG.  2 D″. 
     As shown in FIGS.  2 E and  2 E′, a solder mask layer  24  is formed on the first surface  20   a  of the core board  20  and the circuit layer  21 , and a plurality of openings  240  are formed in the solder mask layer  24  for exposing a part of the circuit layer  21 , thereby allowing the exposed part of the circuit layer  21  to serve as conductive pads  210 . In an embodiment of the present invention, the conductive pads comprise wire bonding pads  210   a  and ball implanting pads  210   b.    
     As shown in FIG.  2 E″, the patterned metal layer  231 ′ formed on the carrier layer  23  is ring-shaped. However, there is no specific restriction on the pattern of the patterned metal layer, as design of the pattern depends on demands. 
     As shown in  FIG. 2F , a conductive seed-layer  25  is formed on the solder mask layer  24 , the conductive pads  210 , a sidewall of the through cavity  200 , the patterned metal layer  231 , and the portion of the carrier layer  23  that covers the end of the through hole  200 . 
     As shown in  FIG. 2G , a resist layer  26  is formed on the conductive seed-layer  25 , and an open area  260  is formed in the resist layer  26  for exposing the conductive seed-layer  25  on the sidewall of the through hole  200 , the patterned metal layer  231 , and the portion of the carrier layer  23  that covers the end of the through hole  200 . A shielding metal layer  27  is formed on the exposed conductive seed-layer  25  by electroplating. 
     As shown in  FIG. 2H , the resist layer  26  and the conductive seed-layer  25  covered thereby are removed to expose the solder mask layer  24  and the conductive pads  210 . 
     As shown in  FIG. 21 , a surface treatment layer  28  is formed on the conductive pads  210  and the shielding metal layer  27 . In an embodiment of the present invention, the surface treatment layer is formed by using freedom chemical plating nickel/gold, Electroless Nickel Immersion Gold (ENIG), Electroless Nickel Electroless Palladium Immersion Gold (ENEPIG), Immersion Tin, or Organic Solderability Preservative (OSP). 
     FIG.  2 I′ depicts a continuing fabrication structure of the structure illustrated in FIG.  2 D′, and FIG.  2 I″ depicts a continuing fabrication structure of the structure illustrated in FIG.  2 D″. 
     In an embodiment of the present invention, an acoustic hole  230  is further formed in the carrier layer  23  passing therethrough for enabling the carrier layer  23  to carry out multi-functional operations. 
     Referring to  FIG. 3 , an embodiment of the present invention using an MEMS carrier as shown in  FIG. 21  is illustrated. As shown, a solder ball  30  is implanted on each of the ball implanting pads  210   b,  and then an MEMS component  31  is mounted on the patterned metal layer  231  in the through hole  200 . The MEMS component  31  is electrically connected to the wire bonding pad  210   a  via conductive wires  33 . In an embodiment of the present invention, a semiconductor component such as an application specific integrated chip (ASIC)  32  is further mounted on the carrier layer  23  in the through hole  200 , and the ASIC  32  is electrically connected to the MEMS component  31  and the wire bonding pad  210   a  via conductive wires  33 . A carrier structure is thus fabricated. 
     Referring to FIG.  3 ′, an MEMS carrier may also be fabricated from a continuing fabrication of the patterned metal layer  231 ′ of FIG.  2 E″, and then the MEMS carrier is applied to mount a sound-controlled MEMS  31 ′ on the patterned metal layer  231 ′ in the through hole  200  thereof. Another carrier structure is thus fabricated. 
     In another embodiment of the present invention, by using a MEMS carrier of FIG.  2 I″, a sound-controlled MEMS component  31 ″ is mounted on the patterned metal layer  231 ″ in the through hole  200 , and yet another carrier structure is thus fabricated, as shown in FIG.  3 ″. 
     The MEMS carrier of the present invention comprises not only the shielding metal layer  27  but also the patterned metal layers  231 ,  231 ′ and  231 ″, and is capable of allocating the MEMS component  31  and the ASIC  32  on the patterned metal layers  231 ,  231 ′, and  231 ″ and the carrier layer  23 . Accordingly, there is no need of the core of a circuit board as in the prior art, thereby efficiently reducing height of the overall structure, and being advantageous in miniaturization of electric products. 
     Furthermore, since the MEMS component  31  is disposed on the patterned metal layer  231 ,  231 ′, and  231 ″, the acoustic hole  230  is thus located under the MEMS component  31 , thereby shortening path of signal received by the MEMS component  31 , and efficiently enhancing signal stability and transmission speed. 
     The present invention further provides an MEMS carrier comprising: a core board  20  having a first surface  20   a  and an opposite second surface  20   b,  a circuit layer  21  formed on the first surface  20   a  and having conductive pads  210 , and at least a through hole  200  formed through the first surface  20   a  and the second surface  20   b;  a carrier layer  23  formed on the second surface  20   b  of the core board  20  and covering an end of the through cavity  200 ; a patterned metal layer  231  formed on a portion of the carrier layer  23  that covers the end of the through hole  200 ; a solder mask layer  24  formed on the first surface  20   a  of the core board  20  and the circuit layer  21 , wherein the solder mask layer  24  has a plurality of openings  240  for exposing the conductive pads  210 ; and a shielding metal layer  27  formed on a sidewall of the through hole  200 , the patterned metal layer  231 , and the portion of the carrier layer  23  that covers the end of the through hole  200 . 
     The conductive pads  210  comprise wire bonding pads  210   a  and ball implanting pads  210   b.    
     In an embodiment of the present invention, the MEMS carrier further comprises an adhering layer  22  disposed between the second surface  20   b  of the core board  20  and the carrier layer  23 . 
     The MEMS carrier layer  23  further comprises a bonding metal layer  232  for attaching the carrier layer  23  to the second surface  20   b  of the core board  20 . 
     The MEMS carrier further comprises a surface treatment layer  28  formed on the conductive pads  210  and the shielding metal layer  27 . In an embodiment of the present invention, the surface treatment layer is formed by using freedom chemical plating nickel/gold, Electroless Nickel Immersion Gold (ENIG), Electroless Nickel Electroless Palladium Immersion Gold (ENEPIG), Immersion Tin, or Organic Solderability Preservative (OSP). 
     In view of the above, according to the MEMS carrier of the present invention and fabrication method of the same, by forming the patterned metal layer on the carrier layer, the MEMS component and ASIC can be mounted on the patterned metal layer and the carrier layer, there is no need to use a circuit board, thereby reducing the height of overall structure and being more advantageous in the miniaturization of electronic products. 
     Furthermore, since the MEMS component is disposed on the patterned metal layer, the acoustic hole thus is located under the MEMS component, thereby shortening path of signal received by the MEMS component, and enhancing signal stability and transmission speed. 
     The invention has been described using exemplary preferred embodiments. However, it is to be understood that the scope of the invention is not limited to the disclosed embodiments. On the contrary, it is intended to cover various modifications and similar arrangements. The scope of the claims, therefore, should be accorded the broadest interpretation so as to encompass all such modifications and similar arrangements.