Abstract:
A package structure having at least an MEMS element is provided, including a chip having electrical connecting pads and the MEMS element; a lid disposed on the chip to cover the MEMS element and having a metal layer provided thereon; first sub-bonding wires electrically connecting to the electrical connecting pads; second sub-bonding wires electrically connecting to the metal layer; an encapsulant disposed on the chip, wherein the top ends of the first and second sub-bonding wires are exposed from the encapsulant; and metallic traces disposed on the encapsulant and electrically connecting to the first sub-bonding wires. The package structure advantageously features reduced size, relatively low costs, diverse bump locations, and an enhanced EMI shielding effect.

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
     This application claims under 35 U.S.C. §119(a) the benefit of Taiwanese Application No. 099101443 filed Jan. 20, 2010 the entire contents of which is incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to package structures, and more particularly, to a package structure having at least a Micro Electro Mechanical System (MEMS) element. 
     2. Description of Related Art 
     Micro Electro Mechanical System (MEMS) techniques integrate electrical and mechanical functions into a single element using microfabrication technology. A MEMS element is disposed on a chip and covered by a shield or packaged with an underfill adhesive so as to form a MEMS package structure.  FIGS. 1A to 1F  are cross-sectional views showing different package structures with a MEMS element. 
       FIG. 1A  shows a package structure disclosed by U.S. Pat. No. 6,809,412. Referring to  FIG. 1A , the package structure comprises a substrate  10 , a chip  14  disposed on the substrate  10  and having a MEMS element  141 , a plurality of bonding wires  11  electrically connecting the substrate  10  and the chip  14 , and a lid  12  disposed on the substrate  10  to cover the chip  14 , the MEMS element  141  and the bonding wires  11 . 
       FIG. 1B  shows a package structure disclosed by U.S. Pat. No. 6,303,986. Referring to  FIG. 1B , the package structure comprises a lead frame  10 ′, a chip  14  disposed on the lead frame  10 ′ and having a MEMS element  141 , a lid  12  disposed on the chip  14  for covering the MEMS element  141 , a plurality of bonding wires  11  electrically connecting the lead frame  10 ′ and the chip  14 , and a packaging material  15  covering the lead frame  10 ′, the bonding wires  11 , the lid  12  and the chip  14 . 
     However, the use of the carriers (the substrate  10  of  FIG. 1A  and the lead frame  10 ′ of  FIG. 1B ) increases the thickness of the overall structures and cannot meet the demand for miniaturization. Accordingly, package structures without a carrier are developed, as shown in  FIGS. 1C to 1D . 
       FIG. 1C  shows a package structure disclosed by U.S. Pat. No. 7,368,808. Referring to  FIG. 1C , the package structure comprises: a chip  14  with electrical connection pads  140 ; a MEMS element  141  disposed on the chip  14 ; and a lid  12  disposed to cover the MEMS element  141 , wherein a plurality of conductive through holes  120  is formed in the lid  12 , and a plurality of contact pads  122  are disposed at the two sides of the conductive through holes  120 , such that the contact pads  122  located at the inner sides of the lid  12  are electrically connected to the electrical connection pads  140  of the chip  14 , respectively. Further, a plurality of solder balls  16  is formed on the contact pads  122  located at the outer sides of the lid  12  for electrically connecting the chip  14  to another electronic element. 
       FIG. 1D  shows a package structure disclosed by U.S. Pat. No. 6,846,725. Referring to  FIG. 1D , the package structure comprises: a chip  14  with electrical connection pads  140 ; a MEMS element  141  disposed on the chip  14 ; and a lid  12  disposed to cover the MEMS element  141 , wherein a plurality of solder bumps  142  is formed on the electrical connection pads  140 , a plurality of conductive through holes  120  is formed in the lid  12  and a plurality of contact pads  122  are disposed at the two sides of the conductive through holes  120 , respectively, and the contact pads  122  located at the inner sides of the lid  12  are electrically connected to the solder bumps  142 , and the contact pads  122  located at the outer sides of the lid  12  are used for electrically connecting the chip  14  to another electronic element. 
     The above structures dispense with a carrier and meet the demand for miniaturization. However, forming the conductive through holes  120  in the lid  12  by drilling incurs high costs. In addition, misalignment or unstable connection can easily occur to the contact pads  122  which flank the conductive through holes  120 , thus leading to poor electrical connection and further adversely affecting the electrical connection quality between the chip  14  and the external electronic element. Accordingly, a package structure dispensing with conductive through holes is provided, as shown in  FIG. 1E . 
       FIG. 1E  shows a package structure disclosed by U.S. Pat. No. 6,828,674. Referring to  FIG. 1E , the package structure comprises: a chip  14  with electrical connection pads  140 ; a MEMS element  141  disposed on the chip  14 ; a lid  12  with traces  121  at an outer side thereof; a support  13  attached to the chip  14  for supporting the lid  12 ; a plurality of bonding wires  11  electrically connecting the traces  121  and the electrical connection pads  140 ; and a packaging material  15  encapsulating the bonding wires  11 , the lid  12  and the chip  14 , wherein the packaging material  15  has an opening  150  for exposing a portion of the traces  121  such that solder balls  16  are formed on the exposed portion of the traces  121  so as to electrically connect to another electronic device. 
     However, the above package structure requires a lithography process for forming the traces on the lid, thus incurring high costs. In addition, the solder balls  16  are confined to the vicinity of the lid to thereby cause solder ball bridge, limit the signal input/output density of the package structure and reduction of the trace spacing, add to the difficulty in attaching the package structure to a circuit board. As such, the application field of the package structure is limited. In addition, corresponding to the package structure, a fine pitch circuit board is required, thus increasing the cost. Further, such a package structure cannot achieve an EMI shielding effect. 
     Therefore, it is imperative to overcome the above drawbacks of the prior art. 
     SUMMARY OF THE INVENTION 
     In view of the above drawbacks of the prior art, the present invention provides a package structure having at least a Micro Electro Mechanical System (MEMS) element, which comprises: a chip having a plurality of electrical connection pads and the at least an MEMS element; a lid disposed on the chip to cover the MEMS element and having a metal layer provided thereon; a plurality of first sub-bonding wires electrically connecting to the electrical connection pads, respectively; a plurality of second sub-bonding wires electrically connecting to the metal layer; an encapsulant disposed on the chip and covering the lid, the first sub-bonding wires and the second sub-bonding wires, wherein the top ends of the first sub-bonding wires and the second sub-bonding wires are exposed from the top surface of the encapsulant; and a plurality of metallic traces disposed on the encapsulant and electrically connecting to the first sub-bonding wires. 
     In another embodiment, the metallic traces are electrically connected to the second sub-bonding wires. 
     The present invention further provides another package structure having at least a Micro Electro Mechanical System (MEMS) element, which comprises: a chip having a plurality of electrical connection pads and the at least an MEMS element; a lid disposed on the chip for covering the MEMS element; a plurality of first sub-bonding wires electrically connecting to the electrical connection pads, respectively; an encapsulant disposed on the chip and covering the lid and the first sub-bonding wires, wherein the top surface of the encapsulant is flush with the top surface of the lid, and the top ends of the first sub-bonding wires are exposed from the top surface of the encapsulant; and a plurality of metallic traces disposed on the encapsulant and electrically connecting to the first sub-bonding wires. 
     The present invention further provides a package structure having at least a Micro Electro Mechanical System (MEMS) element, which comprises: a chip having a plurality of electrical connection pads and the at least an MEMS element; a lid disposed on the chip to cover the MEMS element and having a metal layer provided thereon; a plurality of first sub-bonding wires electrically connecting to the electrical connection pads, respectively; a plurality of second sub-bonding wires electrically connecting to the metal layer; an encapsulant disposed on the chip and covering the lid, the first sub-bonding wires and the second sub-bonding wires, wherein the top ends of the first sub-bonding wires and the second sub-bonding wires are exposed from the top surface of the encapsulant; and a plurality of metallic traces disposed on the encapsulant and composed of first sub-metallic traces and second sub-metallic traces, wherein the first sub-metallic traces electrically connect to the first sub-bonding wires, and the second sub-metallic traces electrically connect to the second sub-bonding wires. 
     According to the present invention, the package structure having at least a Micro Electro Mechanical System (MEMS) element is provided directly on a wafer without the need of a carrier, thus reducing the thickness of the overall structure. Further, the position of the bumps is not limited to the top of the lid. Instead, the bumps are disposed at any positions of the top surface of the package structure. Furthermore, the lid is connected to a ground end through the sub-bonding wires and the metallic traces so as to achieve an EMI shielding effect. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIGS. 1A to 1E  are cross-sectional views showing conventional package structures having a MEMS element; 
         FIGS. 2A to 2F  are cross-sectional views showing a package structure having a MEMS element according to a first embodiment of the present invention, wherein FIGS.  2 E′ and  2 E″ are partially enlarged views showing other embodiments of the structure; 
         FIG. 3  is a cross-sectional view of a package structure having a MEMS element according to a second embodiment of the present invention; 
         FIG. 4  is a cross-sectional view of a package structure having a MEMS element according to a third embodiment of the present invention; 
         FIG. 5  is a cross-sectional view of a package structure having a MEMS element according to a fourth embodiment of the present invention; 
         FIG. 6  is a cross-sectional view of a package structure having a MEMS element according to a fifth embodiment of the present invention; and 
         FIG. 7  is a cross-sectional view of a package structure having a MEMS element according to a sixth embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     The following illustrative embodiments are provided to illustrate the disclosure of the present invention, these and other advantages and effects can be apparent to those in the art after reading this specification. 
     First Embodiment 
       FIGS. 2A to 2F  are cross-sectional views showing a package structure having at least a Micro Electro Mechanical System (MEMS) element according to a first embodiment of the present invention. 
     Referring to  FIG. 2A , a wafer  20  is prepared, which has a plurality of electrical connection pads  201  and a plurality of MEMS elements  202 . It should be noted that only a portion of the wafer is shown in  FIG. 2A . 
     Referring to  FIG. 2B , a plurality of lids  21  is disposed on the wafer  20  for covering the MEMS elements  202 , respectively. The wafer  20  is made of silicon. The MEMS elements  202  are gyroscopes, accelerometers or RF MEMS elements. The lids  21  are made of a conductive material or a non-conductive material such as glass, silicon, metal or ceramic. A metal layer  211  or a plurality of bonding pads, as shown in FIG.  2 B′, is further provided on each of the lids  21  by such as sputtering, which are made of Al, Cu, Au, Pd, Ni/Au, Ni/Pd, TiW/Au, Ti/Al, TiW/Al, Ti/Cu/Ni/Au or a combination thereof. After the formation of the metal layer  211  on each of the lids  21 , cavities are provided on the other side of each of the lids  21 , such that the cavities are opposite to the metal layer  211 . 
     Referring to  FIG. 2C , a plurality of bonding wires  22  electrically connect the electrical connection pads  201  and the metal layer  211 , and an encapsulant  23  is formed on the wafer  20  to cover the lids  21 , the bonding wires  22 , the electrical connection pads  201  and the metal layer  211 . Therein, the encapsulant  23  is made of a dielectric adhesive material such as a thermo-setting resin or silicone, wherein the thermo-setting resin is, for example, an epoxy resin, an epoxy molding compound (EMC) or polyimide. 
     Referring to  FIG. 2D , a portion of the encapsulant  23  is removed, that is, the upper portion of the encapsulant  23  and the top portions of wire loops of the bonding wires  22  are removed such that each of the bonding wires  22  is divided into a first sub-bonding wire  221  and a second sub-bonding wire  222  which are separate from each other. The top ends of the first sub-bonding wires  221  and the second sub-bonding wires  222  are exposed from the top surface of the encapsulant  23 . The first sub-bonding wires  221  are electrically connected to the electrical connection pads  201 . The second sub-bonding wires  222  are electrically connected to the metal layer  211 . The upper portion of the encapsulant  23  is removed by grinding, laser, plasma, chemical etching, or chemical mechanical polishing (CMP.) 
     Referring to  FIG. 2E , a plurality of metallic traces  24  is provided on the encapsulant  23  to electrically connect to the first sub-bonding wires  221 , respectively, and electrically isolate the second sub-bonding wires  222 . In addition, one end of each of the metallic traces  24  is configured to extend towards the corresponding MEMS element  202  or the periphery of the MEMS element  202  (not shown.) The layout of the metallic traces  24  is flexibly adjusted according to the electrical demands and layout density limit. Furthermore, bumps  25  are provided on the metallic traces  24 . For example, the bumps  25  are provided on the ends of the metallic traces  24 . The bumps  25  are made of metal or alloy, and have soldering characteristics. The bumps  25  are preferably made of Sn/Pd, Sn/Ag/Cu or Au. Referring to FIG.  2 E′, prior to formation of the bumps  25 , a first insulation layer  240   a  is provided on the encapsulant  23  and the metallic traces  24 . The first insulation layer  240   a  has a plurality of openings  2401  for exposing the metallic traces  24 . The bumps  25  are provided at the openings  2401  for electrically connecting to the metallic traces  24 . In addition, prior to formation of the metallic traces  24 , a second insulation layer  240   b  is provided on the encapsulant  23 . The second insulation layer  240   b  has a plurality of openings  2402  for exposing the first sub-bonding wires  221  and electrically isolating the second sub-bonding wires  222 . The structure shown in FIG.  2 E′ is achieved through redistribution layer (RDL) technique. 
     An insulation layer (not shown,) such as green paint, is formed before the bumps  25  are formed. The insulation layer has a plurality of openings for exposing the metallic traces  24  such that the bumps  25  are electrically connected to the exposed metallic traces  24 . 
     In another embodiment as shown in FIG.  2 E″, the second insulation layer  240   b  has a plurality of openings  2402  for exposing the second sub-bonding wires  222  and electrically isolating the first sub-bonding wires  221 , and the metallic traces  24  electrically connect to the second sub-bonding wires  222 . A first insulation layer  240   a  is provided on the encapsulant  23  and the metallic traces  24  and has a plurality of openings  2401  for exposing the metallic traces  24 , and the bumps  25  are provided at the openings  2401  for electrically connecting to the metallic traces  24 . The layout of the metallic traces  24  is designed to stay away from the top of the second sub-bonding wires  222  to achieve an electrical isolation effect (not shown.) 
     Furthermore, an under bump metal layer  26  is formed at the openings  2401  of the first insulation layer  240   a  before the bumps  25  are formed. 
     Referring to  FIG. 2F , a singulation process is performed to obtain a plurality of package structures  2  each having a MEMS element  202 . 
     The present invention further discloses a package structure  2  having a MEMS element, which comprises: a chip  20 ′ having a plurality of electrical connection pads  201  and at least a MEMS element  202 ; a lid  21  disposed on the chip  20 ′ for covering the MEMS element  202  and having a metal layer  211  provided thereon; a plurality of first sub-bonding wires  221  electrically connecting to the electrical connection pads  201 ; a plurality of second sub-bonding wires  222  electrically connecting to the metal layer  211 ; an encapsulant  23  disposed on the chip  20 ′ and covering the lid  21 , the first sub-bonding wires  221  and the second sub-bonding wires  222 , wherein the top ends of the first sub-bonding wires  221  and the second sub-bonding wires  222  are exposed from the top surface of the encapsulant  23 ; and a plurality of metallic traces  24  disposed on the encapsulant  23  and electrically connecting to the first sub-bonding wires  221 . 
     In another embodiment, as shown in FIG.  2 E″, the metallic traces  24  are disposed on the encapsulant  23  and electrically connecting to the second sub-bonding wires  222 . In a preferred embodiment, the packaging structure  2  further comprises a first insulation layer  240   a  provided on the encapsulant  23  and the metallic traces  24  and having a plurality of openings  2401  for exposing the metallic traces  24 , and a plurality of bumps  25  is formed at the openings  2401  for electrically connecting to the metallic traces  24 . The packaging structure  2  further comprises a second insulation layer  240   b  on the encapsulant  23  and having openings  2402  for exposing the first sub-bonding wires  221  or the second sub-bonding wires  222  such that the metallic traces  24  are provided in the openings  2402  and on the second insulation layer  240   b.    
     In the embodiment where the first insulation layer  240   a  is provided, the package structure  2  further comprises an under bump metal layer  26  formed between the bumps  25  and the first insulation layer  240   a.    
     In the package structure  2  having a MEMS element of the present invention, each of the metallic traces  24  has one end extending towards the corresponding MEMS element  202  and having a bump  25  provided thereon. To be specific, the metallic traces  24  essentially extend from the electrical connection pads  201  to the MEMS elements  202 . 
     In the package structure  2 , the chip  20 ′ is made of silicon. The MEMS element  202  is a gyroscope, an accelerometer or a RF MEMS element. The lid  21  is made of a conductive material or a non-conductive material such as metal, silicon, glass or ceramic. The metal layer  211  is made of Al, Cu, Au, Pd, Ni/Au, Ni/Pb, TiW/Au, Ti/Al, TiW/Al, Ti/Cu/Ni or a combination thereof. The package layer  23  is made of a dielectric adhesive material such as a thermo-setting resin or silicone. The thermo-setting resin is, for example, an epoxy resin, an epoxy molding compound (EMC) or polyimide. 
     In the case the metallic traces are electrically isolated from the second sub-bonding wires, one end of each of the metallic traces  24  extends towards the MEMS element  202  and even extends to the lid. At a position where the bottom of the metallic traces  24  is adjacent to the second sub-bonding wires  222 , an insulation pad made of the same material as the second insulation layer  240   b  is configured to electrically isolate the second sub-bonding wires  222 . Similarly, in the case the metallic traces are electrically isolated from the first sub-bonding wires, an insulation pad is disposed at a position where the bottom of the metallic traces  24  is adjacent to the first sub-bonding wires  221 . 
     In the package structure  2 , the electrical connection pads  201  are located at the outer periphery of the lid  21 . 
     In the package structure  2 , the bumps  25  are made of metal or alloy and having soldering characteristics. The bumps  25  are preferably made of Sn/Pb, Sn/Ag or Au. 
     Second Embodiment 
       FIG. 3  is a cross-sectional view of a package structure  3  having a MEMS element according to a second embodiment of the present invention. The package structure  3  of  FIG. 3  is similar to the package structure  2  of  FIG. 2F , but the main difference therebetween is that the metal layer  211  of the package structure  3  is composed of a plurality of bonding pads, and the metallic traces  24  electrically connect to the first sub-bonding wires  221  and the second sub-bonding wires  222 , respectively. 
     Third Embodiment 
       FIG. 4  is a cross-sectional view of a package structure  4  having a MEMS element according to a third embodiment of the present invention. The package structure  4  in the third embodiment is similar to the package structure  2  of  FIG. 2F , but a main difference therebetween is that the top surface of the encapsulant  23  of the package structure  4  is flush with the top surface of the lid  21 , i.e., the metal layer  211  is exposed from the encapsulant  23 , and the second sub-bonding wires  222  are removed at the time a portion of the encapsulant  23  is removed. As such, the first sub-bonding wires  221  are remained for electrically connecting to the electrical connection pads  201 , and the top ends of the first sub-bonding wires  221  are exposed from the top surface of the encapsulant  23 . 
     Fourth Embodiment 
       FIG. 5  is a cross-sectional view of a package structure  5  having a MEMS element according to a fourth embodiment of the present invention. The package structure  5  in the fourth embodiment is similar to the package structure  4  in  FIG. 4 , but a big difference therebetween is that the metal layer  211  of the package structure  5  is removed at the time a portion of the encapsulant  23  is removed, and the metallic traces  24  extend to the lid  21 . 
     Fifth Embodiment 
       FIG. 6  is a cross-sectional view of a package structure  6  having a MEMS element according to a fifth embodiment of the present invention. The package structure  6  in the fifth embodiment is similar to the package structure  5  in  FIG. 5 , but the main difference therebetween is that the metallic traces  24  extend on the lid  21 . 
     Sixth Embodiment 
       FIG. 7  is a cross-sectional view of a package structure  7  having a MEMS element according to a sixth embodiment of the present invention. The package structure  7  in the sixth embodiment is similar to the package structure  2  of  FIG. 2F , but the main differences therebetween include: the metallic traces  24  of the package structure  7  in the sixth embodiment are separated into first sub-metallic traces  241  electrically connecting to the first sub-bonding wire  221  and second sub-metallic traces  242  electrically connecting to the second sub-bonding wire  222 ; each of the first sub-metallic traces  241  has one end extending towards the periphery of the chip  20 ′ and having a bump  251  provided thereon; and each of the second sub-metallic traces  242  has one end extending towards the periphery of the MEMS element  202  and having a bump  252  provided thereon. 
     Referring to FIG.  2 E′ again, the package structure  7  further comprises a first insulation layer provided on the encapsulant and the metallic traces and having a plurality of openings for exposing the metallic traces. The package structure  7  further comprises a second insulation layer (not shown) provided on the encapsulant and having a plurality of openings for exposing the first and second sub-bonding wires such that the metallic traces are provided in the openings and on the second insulation layer. 
     In the package structure  7 , the second sub-bonding wires  222 , the second sub-metallic traces  242  and the bumps  252  are grounded for achieving an EMI shielding effect. 
     According to the present invention, the package structure having a MEMS element is provided directly on a wafer without the need of a carrier, thus reducing the thickness of the overall structure. Further, the position of the bumps is not limited to the top of the lid. Instead, the bumps are disposed at any positions of the top surface of the package structure. Furthermore, the lid is connected to a ground end through the sub-bonding wires and the metallic traces so as to achieve an EMI shielding effect. 
     The above-described descriptions of the detailed embodiments are intended to illustrate the preferred implementation according to the present invention but are not intended to limit the scope of the present invention, Accordingly, all modifications and variations completed by those with ordinary skill in the art should fall within the scope of present invention defined by the appended claims.