Abstract:
A fabrication method of a semiconductor package structure includes: patterning a metal plate having first and second surfaces; forming a dielectric layer on the metal plate; forming a metal layer on the first surface and the dielectric layer; forming metal pads on the second surface, the metal layer having a die pad and traces each having a bond pad; mounting a semiconductor chip on the die pad, followed by connecting electrically the semiconductor chip to the bond pads through bonding wires; forming an encapsulant to cover the semiconductor chip and the metal layer; removing portions of the metal plate not covered by the metal pads so as to form metal pillars; and performing a singulation process. The fabrication method is characterized by disposing traces with bond pads close to the die pad to shorten the bonding wires and forming metal pillars protruding from the dielectric layer to avoid solder bridging.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to fabrication methods of semiconductor package structures, and more particularly, to a fabrication method of a semiconductor package structure characterized by high quality of wire bonding but not susceptible to solder bridging. 
         [0003]    2. Description of Related Art 
         [0004]    In a conventional lead frame based semiconductor package such as a QFN (Quad Flat Non-lead) package, a semiconductor chip is attached and wire-bonded to a lead frame and encapsulated by an encapsulant, and metal portions around the lead frame are exposed from the encapsulant to serve as contact pads for connection with an external device. A semiconductor package structure thus fabricated is advantageously characterized by reduced size, improved electrical performance, and wide application in the industry. 
         [0005]      FIG. 1A  shows a conventional fabrication method of a semiconductor package structure as disclosed by U.S. Pat. No. 6,143,981, No. 6,424,024, No. 6,414,385, No. 5,942,794, No. 6,420,779, No. 6,399,415 and No. 6,291,274. 
         [0006]    Referring to  FIG. 1A , a semiconductor chip  11  is disposed on a lead frame  10  and electrically connected to contact pads  101  peripherally provided on the lead frame  10  through bonding wires  12 , and an encapsulant  13  is formed on the lead frame  10  to encapsulate the semiconductor chip  11  and the bonding wires  12 , thereby allowing the side surfaces and bottom surfaces of the contact pads  101  to be exposed from the encapsulant  13 . 
         [0007]      FIG. 1B  is a side view of the semiconductor package structure  1  of  FIG. 1A  connected to a circuit board  15 . Referring to  FIG. 1B , the contact pads  101  are connected to solder pads  151  of the circuit board  15  through a solder material  14 . However, since the contact pads are closely arranged and do not protrude from the bottom surface of the semiconductor package structure  1 , when the semiconductor package structure  1  is soldered to the circuit board  15 , the gap between the contact pads  101  and the solder pads  151  of the circuit board  15  is so small that it is difficult to control the gap. As a result, the reliability of the solder joints is low, the solder joints are easy to crack, and the soldering situation is difficult to check. Due to the small gap between the semiconductor package structure  1  and the circuit board  15 , the solder material  14  overflows readily to thereby cause solder bridging. 
         [0008]    Further, the semiconductor package structure  1  cannot provide array arranged contact pads and accordingly cannot provide a semiconductor package structure with high density I/O connections. 
         [0009]    Accordingly, U.S. Pat. No. 6,498,099, No. 7,049,177, No. 6,238,952, No. 6,700,188 and No. 6,777,265 disclose a fabrication method of a semiconductor package structure, as shown in  FIGS. 2A and 2B . 
         [0010]      FIG. 2A  is a cross-sectional view of a conventional fabrication method of a semiconductor package structure  2  and  FIG. 2B  is a top view of the semiconductor package structure  2 . Referring to  FIGS. 2A and 2B , half of the thickness of the lead frame  20  is etched away; a semiconductor chip  21  is disposed on the lead frame  20  and electrically connected to contact pads  201  peripherally provided on the lead frame  20  through bonding wires  22 ; an encapsulant  23  is formed on the lead frame  20 ; and then the semiconductor package structure  2  is etched for a second time such that each of the contact pads  201  protrudes from the bottom of the semiconductor package structure  2  by about half of the thickness of the lead frame  20 . Further, the contact pads  201  can be arranged in array. 
         [0011]    However, although a certain gap is provided between the contact pads and the circuit board and array-arranged contact pads are provided, since long bonding wires are required to electrically connect the semiconductor chip to the contact pads located far away, it adversely affects the electrical performance of the package structure. Further, due to tangling of the bonding wires, it is difficult for the package structure to provide high density I/O connections. 
         [0012]    Therefore, it is imperative to overcome the above drawbacks of the prior art. 
       SUMMARY OF THE INVENTION 
       [0013]    In view of the above drawbacks of the prior art, the present invention provides a fabrication method of a semiconductor package structure. The fabrication method comprises the steps of: providing a metal plate having a first surface and an opposite second surface, wherein the first surface has a die mounting area and a plurality of contact pad areas; patterning the metal plate from the first surface towards the second surface so as to form a plurality of concave portions in the metal plate outside the die mounting area and the contact pad areas; forming a dielectric layer on the patterned metal plate, the die mounting area and the contact pad areas being exposed from the dielectric layer; forming a metal layer on the first surface and the dielectric layer and forming a plurality of metal pads on the second surface, wherein the metal layer comprises a die pad corresponding in position to the die mounting area and a plurality of traces, each of the traces comprises a trace body, a bond pad extending towards the periphery of the die pad and a trace end opposite to the bond pad and connecting to a corresponding one of the contact pad areas, and the metal pads correspond in position to the die mounting area and the contact pad areas, respectively; disposing a semiconductor chip on the die pad and electrically connecting the semiconductor chip to the bond pads through a plurality of bonding wires; forming an encapsulant to cover the semiconductor chip, the bonding wires, the metal layer, and the dielectric layer; removing the portions of the metal plate not covered by the metal pads so as to form a plurality of metal pillars corresponding in position to the die mounting area and the contact pad areas, respectively, wherein the metal pillars protrude from the dielectric layer; and performing a singulation process to obtain a semiconductor package structure. 
         [0014]    In the above-described method, the step of forming the dielectric layer can further comprise coating a dielectric layer on the patterned metal plate and grinding the dielectric layer so as to make the dielectric layer be flush with the surfaces of the die mounting area and the contact pad areas. 
         [0015]    The step of forming the metal layer on the first surface and the dielectric layer can comprise: forming a first resist layer on the first surface and the dielectric layer and forming a plurality of first open areas in the first resist layer; forming the metal layer in the first open areas; and removing the first resist layer. 
         [0016]    The step of forming the metal pads on the second surface can comprise: forming a second resist layer on the second surface and forming a plurality of second open areas in the second resist layer corresponding in position to the die mounting area and the contact pad areas; forming the metal pads in the second open areas; and removing the second resist layer. 
         [0017]    In the above-described method, the metal plate can be made of copper, and the dielectric layer can be made of a polymer material comprising an epoxy resin. The metal layer and the metal pads can be formed by an electroplating process and can be made of one or more selected from the group consisting of Au, Pd, and Ni. 
         [0018]    In addition, the contact pad areas are arranged in array to surround the die mounting area, and the bond pads are disposed at the periphery of the die pad, thereby shortening the bonding wires electrically connecting the semiconductor chip and the bond pads. 
         [0019]    The present invention further discloses a fabrication method of a semiconductor package structure. The fabrication method comprises the steps of: providing a metal plate having a first surface and an opposite second surface, wherein the first surface has a die mounting area and a plurality of contact pad areas; patterning the metal plate from the first surface towards the second surface so as to form a plurality of concave portions in the metal plate outside the contact pad areas; forming a dielectric layer on the patterned metal plate, the contact pad areas being exposed from the dielectric layer; forming a plurality of traces on the first surface and the dielectric layer and forming a plurality of metal pads on the second surface, wherein each of the traces comprises a trace body, a bond pad extending into the die mounting area and a trace end opposite to the bond pad and connecting to a corresponding one of the contact pad areas, and the metal pads correspond in position to the contact pad areas, respectively; mounting a semiconductor chip on the bond pads for electrical connection with the traces; forming an encapsulant to cover the semiconductor chip, the traces and the dielectric layer; removing the portions of the metal plate that are not covered by the metal pads so as to form a plurality of metal pillars corresponding in position to the contact pad areas, respectively, wherein the metal pillars protrude from the dielectric layer, respectively; and performing a singulation process to obtain a semiconductor package structure. 
         [0020]    According to the present invention, the bond pads and traces formed at the chip mounting side of the dielectric layer shorten the bonding wires and prevent tangling of the bonding wires, thereby improving the electrical connection quality of the package structure. Further, when the semiconductor package structure is soldered to a circuit board, since the metal pillars protrude from the bottom surface of the dielectric layer, it facilitates the formation of stable solder joints between the metal pillars and the circuit board and prevents solder overflow and bridging. In addition, the present invention provides high density and array arranged I/O connections so as to extend the application range of the semiconductor package structure. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0021]      FIG. 1A  is a cross-sectional view of a conventional fabrication method of a semiconductor package structure; 
           [0022]      FIG. 1B  is a side view of the semiconductor package structure of  FIG. 1A  connecting to a circuit board; 
           [0023]      FIGS. 2A and 2B  are a cross-sectional view and top view of another conventional fabrication method of a semiconductor package structure; 
           [0024]      FIGS. 3A to 3G  are cross-sectional views showing a fabrication method of a semiconductor package structure according to a preferred embodiment of the present invention, wherein FIG.  3 E′ is a top view,  FIG. 3E  is a cross-sectional view taken along line  3 E- 3 E of FIG.  3 E′; and 
           [0025]      FIGS. 4A to 4G  are cross-sectional views showing a fabrication method of a semiconductor package structure according to another embodiment of the present invention, wherein FIG.  4 E′ is a top view,  FIG. 4E  is a cross-sectional view taken along line  4 E- 4 E of FIG.  4 E′. 
       
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0026]    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. 
         [0027]      FIGS. 3A to 3G  are cross-sectional views showing a fabrication method of a semiconductor package structure according to a preferred embodiment of the present invention, wherein FIG.  3 E′ is a top view, and  FIG. 3E  is a cross-sectional view taken along line  3 E- 3 E of FIG.  3 E′. 
         [0028]    Referring to  FIG. 3A , a metal plate  30  having a first surface  30   a  and an opposite second surface  30   b  is provided, wherein the first surface  30   a  has a die mounting area  301  and a plurality of contact pad areas  302 . The metal plate  30  can be made of copper. 
         [0029]    Referring to  FIG. 3B , the metal plate  30  is patterned from the first surface  30   a  towards the second surface  30   b  so as to form a plurality of concave portions  300  in the metal plate  30  outside the die mounting area  301  and the contact pad areas  302 , wherein the concave portions  300  surrounding the die mounting area  301  and the contact pad areas  302 . The patterning of the metal plate  30  or the formation of the concave portions  300  can be implemented by means of a resist layer (not shown) and performed by an etching process. Since such a technique is well known in the art, detailed description thereof is omitted herein. 
         [0030]    Referring to  FIG. 3C , a dielectric layer  31  is formed on the patterned metal plate  30 , with the die mounting area  301  and the contact pad areas  302  exposed from the dielectric layer  31 . Specifically speaking, a dielectric layer  31  is coated in the concave portions  300  and on the first surface  30   a , and then a portion of the dielectric layer  31  which is higher than the first surface  30   a  is removed to expose the die mounting area  301  and the contact pad areas  302 . The dielectric layer  31  can be made of a polymer material comprising an epoxy resin. In addition, the higher portion of the dielectric layer  31  can be removed by a grinding process such that the dielectric layer  31  thus ground is flush with the surfaces of the die mounting area  301  and the contact pad areas  302 . 
         [0031]    Referring to  FIG. 3D , a first resist layer  32   a  is formed on the first surface  30   a  and the dielectric layer  31 , and a plurality of first open areas  320   a  is formed in the first resist layer  32   a ; meanwhile, a second resist layer  32   b  is formed on the second surface  30   b , and a plurality of second open areas  320   b  is formed in the second resist layer  32   b  such that the second open areas  320   b  thus formed correspond in position to the die mounting area  301  and the contact pad areas  302 , respectively. 
         [0032]    Referring to FIGS.  3 E and  3 E′, a metal layer  33  is formed in the first open areas  320   a , and a plurality of metal pads  34  is formed in the second open areas  320   b , respectively. The metal layer  33  comprises a die pad  333  corresponding in position to the die mounting area  301  and a plurality of traces  332 . Each of the traces  332  comprises a trace body  3321 , a bond pad  3322  extending to the periphery of the die pad  333 , and a trace end  3323  opposite to the bond pad  3322  and connected to a corresponding one of the contact pad areas  302 . The metal pads  34  correspond in position to the die mounting area  301  and the contact pad areas  302 , respectively. Thereafter, the first resist layer  32   a  and the second resist layer  32   b  are removed. The metal layer  33  and the metal pads  34  can be formed by an electroplating process and can be made of one or more selected from the group consisting of Au, Pd, and Ni, for example, Au/Pd/Ni/Pd. 
         [0033]    The fabrication method of the present invention is not limited by the sequence in which the metal layer and the metal pads are formed, because it is feasible to form the metal layer and the metal pads concurrently by an electroplating process despite the variable sequence in which the first resist layer and the second resist layer are formed. 
         [0034]    Referring to FIG.  3 E′, the contact pad areas  302  are arranged in array to surround the die mounting area  301 , and the bond pads  3322  are disposed at the periphery of the die pad  333  to surround the die pad  333 . 
         [0035]    Referring to FIG.  3 E′, the metal pillars  303  are arranged in array to surround the die pad  333 , and preferably, the bond pads  3322  are disposed at the periphery of the die pad  333  to surround the die pad  333 . 
         [0036]    Referring to  FIG. 3F , a semiconductor chip  35  is mounted on the die pad  333  and electrically connected to the bond pads  3322  through a plurality of bonding wires  36 , and an encapsulant  37  is formed to cover the semiconductor chip  35 , the bonding wires  36 , the metal layer  33  and the dielectric layer  31 . 
         [0037]    Referring to  FIG. 3G , the portions of the metal plate  30  that are not covered by the metal pads  34  are removed so as to form a plurality of metal pillars  303  corresponding in position to the die mounting area  301  and the contact pad areas  302  and protruding from the dielectric layer  31 . Finally, a singulation process is performed to obtain a semiconductor package structure  3 . 
         [0038]      FIGS. 4A to 4G  are cross-sectional views showing a fabrication method of a semiconductor package structure according to another embodiment of the present invention, wherein FIG.  4 E′ is a top view, and  FIG. 4E  is a cross-sectional view taken along line  4 E- 4 E of FIG.  4 E′. 
         [0039]    Referring to  FIG. 4A , a metal plate  40  having a first surface  40   a  and an opposite second surface  40   b  is provided, wherein the first surface  40   a  has a die mounting area  401  and a plurality of contact pad areas  402 . The metal plate  40  can be made of copper. 
         [0040]    Referring to  FIG. 4B , the metal plate  40  is patterned from the first surface  40   a  towards the second surface  40   b  so as to form a plurality of concave portions  400  in the metal plate  40  outside the contact pad areas  402 , respectively. The patterning of the metal plate  40  or the formation of the concave portions  4300  can be implemented by means of a resist layer (not shown) and performed by an etching process. Since such a technique is well known in the art, detailed description thereof is omitted herein. 
         [0041]    Referring to  FIG. 4C , a dielectric layer  41  is formed on the patterned metal plate  40 , with the contact pad areas  402  exposed from the dielectric layer  41 . Specifically speaking, a dielectric layer  41  is coated in the concave portions  400  and on the first surface  40   a , and then a portion of the dielectric layer  41  which is higher than the first surface  40   a  is removed to expose the contact pad areas  402 . The dielectric layer  41  can be made of a polymer material comprising an epoxy resin. In addition, the dielectric layer  41  can be removed by a grinding process such that the dielectric layer  41  thus ground is flush with the surfaces of the contact pad areas  402 . 
         [0042]    Referring to  FIG. 4D , a first resist layer  42   a  is formed on the first surface  40   a  and the dielectric layer  41 , and a plurality of first open areas  420   a  is formed in the first resist layer  42   a ; meanwhile, a second resist layer  42   b  is formed on the second surface  40   b , and a plurality of second open areas  420   b  is formed in the second resist layer  42   b  such that the second open areas  420   b  thus formed correspond in position to the contact pad areas  402 , respectively. 
         [0043]    Referring to FIGS.  4 E and  4 E′, a plurality of traces  432  is formed in the first open areas  420   a , and a plurality of metal pads  44  is formed in the second open areas  420   b . Each of the traces  432  comprises a trace body  4321 , a bond pad  4322  extending into the die mounting area  401 , and a trace end  4323  opposite to the bond pad  4322  and connected to a corresponding one of the contact pad areas  402 . The metal pads  44  correspond in position to the contact pad areas  402 , respectively. Thereafter, the first resist layer  42   a  and the second resist layer  42   b  are removed. The traces  432  and the metal pads  44  can be formed by an electroplating process and can be made of one or more selected from the group consisting of Au, Pd, and Ni, for example, Au/Pd/Ni/Pd. 
         [0044]    The fabrication method of the present invention is not limited by the sequence in which the plurality of traces and the plurality of metal pads are formed, because it is feasible to form the plurality of traces and the plurality of metal pads concurrently by an electroplating process despite the variable sequence in which the first resist layer and the second resist layer are formed. 
         [0045]    Referring to FIG.  4 E′, the contact pad areas  402  can be arranged in array to surround the die mounting area  401 , and the bond pads  4322  can be arranged in array in the die mounting area  401 . 
         [0046]    Referring to FIG.  4 E′, the metal pillars  403  can be arranged in array to surround the die mounting area  401 , and preferably, the bond pads  4322  are annularly arranged within the die mounting area  401 . 
         [0047]    Referring to  FIG. 4F , a semiconductor chip  45  is flip-chip mounted on the bond pads  4322  so as to be electrically connected to the traces  432 , and an encapsulant  47  is formed to cover the semiconductor chip  45 , the traces  432  and the dielectric layer  41 . 
         [0048]    Referring to  FIG. 4G  the portions of the metal plate  40  that are not covered by the metal pads  44  are removed so as to form a plurality of metal pillars  403  corresponding in position to the contact pad areas  402  and protruding from the dielectric layer  41 . Finally, a singulation process is performed to obtain a semiconductor package structure  4 . 
         [0049]    According to the present invention, the bond pads and traces formed at the chip mounting side of the dielectric layer shorten the bonding wires and prevent tangling of the bonding wires, thereby improving the electrical connection quality of the package structure. Further, when the semiconductor package structure is soldered to a printed circuit board, since the metal pillars protrude from the bottom surface of the dielectric layer, it facilitates the formation of stable solder joints between the metal pillars and the printed circuit board and prevents solder overflow and bridging. In addition, the present invention provides high density and array arranged I/O connections so as to extend the application range of the semiconductor package structure. 
         [0050]    The above description of the specific embodiments is intended to illustrate the preferred implementation according to the present invention but is 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.