Abstract:
An improved dual die package is disclosed. The dual die package includes a first lead frame connected to a first semiconductor chip and a second lead frame connected to a second semiconductor chip. The first leads and the second leads are electrically connected to one another using a wirebonding process rather than a thermocompression process thereby allowing conventional packaging equipment to be used when manufacturing a dual die package.

Description:
BACKGROUND  
         [0001]    1. Field of the Invention  
           [0002]    The present invention relates to semiconductor packaging and, more particularly, to a dual die package (DDP).  
           [0003]    2. Description of the Related Arts  
           [0004]    Recent trends in electronics development have been toward smaller and thinner semiconductor packages. To satisfy the demand for smaller and thinner semiconductor packages, semiconductor packages that contain multiple semiconductor dies or chips (“multi-chip packages”) have been developed. Multi-chip packages are used in a wide variety of applications, such as in laptop computers and cellular phones. When compared with single-chip packages, multi-chip packages have the advantages of miniaturization, low weight and high mounting density. For example, it is more advantageous to use a single thin small outline package (TSOP) including a flash memory chip and a SRAM chip than a semiconductor package including the flash memory chip and another semiconductor package including the SRAM chip.  
           [0005]    Multi-chip packages can be classified as vertical-stacking type packages or parallel-aligning type packages. Vertical-stacking type packages reduce mounting area, while parallel-aligning type packages simplify the manufacturing process and reduce package thickness. To achieve miniaturization and low weight, vertical-stacking type packages are more commonly used.  
           [0006]    [0006]FIG. 1 is a cross-sectional view of a conventional dual die package  200 , which is a vertical-stacking type package. Dual die package  200  comprises a first chip  110  and a second chip  130 . First chip  110  has electrode pads  112  on a center region of its active surface, and second chip  130  has electrode pads  132  on a center region of its active surface. Second leads  141  are mechanically connected to the active surface of second chip  130  via an adhesive  152 , and first leads  121  are mechanically connected to the active surface of first chip  110  by an adhesive  152 .  
           [0007]    Second chip  130  is attached to the bottom surfaces of second leads  141  such that electrode pads  132  are located between the opposite second leads  141 , and first chip  110  is attached to the bottom surfaces of first leads  121  such that electrode pads  112  are located between the opposite first leads  121 . The back surfaces of first chip  110  and second chip  130  face one another and are disposed between first leads  121  and second leads  141 .  
           [0008]    First leads  121  comprise first contact portions  123  and first connection portions  125 . First connection portions  125  are stepwise connected to first contact portions  123 . Second leads  141  comprise second contact portions  143  and second connection portions  145 . Second connection portions  145  are stepwise connected to second contact portions  143 .  
           [0009]    Electrode pads  112  of first chip  110  are electrically connected to first contact portions  123  via bonding wires  162 , and electrode pads  132  of second chip  130  are electrically connected to second contact portions  143  via bonding wires  164 . First chip  110 , second chip  130  and the electrical connection parts are encapsulated with an encapsulant, thereby forming a package body  180 .  
           [0010]    First connection portions  125  of first leads  121  and second connection portions  145  of second leads  141  are mechanically attached to each other and electrically connected to each other. Outer lead portions (not shown) of first leads  121  are cut and removed. Outer lead portions  149  of second leads  141  are bent in a predetermined shape so that they can be mounted and serve as external connection terminals. After forming a metal layer  170  made of a metal such as solder or silver (Ag) on first connection portions  125  and second connection portions  145 , the first connection portions  125  are attached to the corresponding second connection portions  145  using a thermocompression process carried out at a predetermined temperature and pressure. The thermocompression process mechanically and electrically connects first connection portions  125  and second connection portions  145 .  
           [0011]    One disadvantage with manufacturing conventional dual die package  200  is that the step of forming metal layer  170  on first leads  121  and second leads  141  and the step of attaching first leads  121  and second leads  141  using a thermocompression process to each other require additional manufacturing equipment, which increases the production cost of conventional dual die package  200 . Another disadvantage with manufacturing conventional dual die package  200  is that the thermocompression process used to attach the first leads  121  of the first lead frame  120  to the second leads  141  of the second lead frame  140  requires highly reliable attaching technology, which increases the production cost of conventional dual die package  200 .  
           [0012]    Accordingly, what is needed is an improved dual die package.  
         SUMMARY  
         [0013]    The present invention provides an improved dual die package. In one embodiment, a dual die package includes a first semiconductor chip having a back surface, a second semiconductor chip having a back surface that faces the back surface of the first semiconductor chip, a first lead frame having a plurality of first leads disposed over and electrically coupled to an active surface of the first semiconductor chip, a second lead frame having a plurality of second leads disposed over and electrically coupled to an active surface of the second semiconductor chip, and bonding wires that electrically connect the first leads to the second leads.  
           [0014]    Other embodiments, aspects, and advantages of the present invention will become apparent from the following descriptions and the accompanying drawings. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0015]    For a more complete understanding of the present invention and for further embodiments, aspects, and advantages, reference is now made to the following description taken in conjunction with the accompanying drawings in which:  
         [0016]    [0016]FIG. 1 is a cross-sectional view of a conventional dual die package;  
         [0017]    [0017]FIG. 2 is a perspective view showing wire bonding of a dual die package in accordance with an embodiment of the present invention;  
         [0018]    [0018]FIG. 3 is a cross-sectional view of the dual die package of FIG. 2 in accordance with an embodiment of the present invention;  
         [0019]    [0019]FIG. 4 is a bottom plan view of the dual die package of FIG. 2; and  
         [0020]    [0020]FIG. 5 is a top plan view of the dual die package of FIG. 2. 
     
    
     DETAILED DESCRIPTION  
       [0021]    [0021]FIG. 2 is a perspective view showing wire bonding of a dual die package  100  in accordance with an embodiment of the present invention. FIG. 3 is a cross-sectional view of dual die package  100 .  
         [0022]    As shown in FIGS. 2 and 3, dual die package  100  comprises a first chip  10  and a second chip  30 . First chip  10  has a plurality of electrode pads  12  located at a center region of its active surface and second chip  30  has plurality of electrode pads  32  located at a center region of its active surface. The back surface of first chip  10  faces and is mounted to the back surface of second chip  30 . First leads  21  of a first lead frame  20  are attached to the active surface of first chip  10 , and second leads  41  of a second lead frame  40  are attached to the active surface of second chip  30 . First leads  21  are electrically connected to electrode pads  12  of first chip  10  via bonding wires  62 , and second leads  41  are electrically connected to electrode pads  32  of the second chip  30  via bonding wires  64 . First chip  10 , second chip  30  and the electrical connection parts are encapsulated with a liquid molding resin, thereby forming a package body  80 .  
         [0023]    As described in more detail below, the active surface of second chip  30  is attached to the bottom surface of inner terminals of second leads  41  by an adhesive tape  52 , and the active surface of first chip  10  is attached to the bottom surface of inner terminals of first leads  21  by an adhesive tape  52 . Electrode pads  32  of second chip  30  are located between opposite second leads  41 , and electrode pads  12  of first chip  10  are located between opposite first leads  21 . The back surfaces of first chip  10  and second chip  30  face one another and are located between first leads  21  and second leads  41 . First leads  21  comprise first contact portions  23  and first connection portions  25 , and second leads  41  comprise second contact portions  43  and second connection portions  45 .  
         [0024]    Electrode pads  12  of first chip  10  are electrically connected to first contact portions  23  of first leads  21  by first bonding wires  62 , and electrode pads  32  of second chip  30  are electrically connected to second contact portions  43  of second leads  41  by second bonding wires  64 . The surfaces of first contact portions  23  and second contact portions  43  can be plated with silver (Ag), thereby obtaining excellent bondability between first and second bonding wires  62  and  64  and first and second contact portions  23  and  43 , respectively.  
         [0025]    [0025]FIG. 4 is a bottom plan view of the dual die package  100  of FIG. 2. First lead frame  20  for a lead-on-chip (LOC) package includes connection pads  27 . Each connection pad  27  protrudes from the side surface of a corresponding first connection portion  25 . An outer terminal of the first connection portion  27  is connected to a side rail  24 . An adhesive layer  54  (shown in FIG. 2) is discontinuously formed along side rail  24  of the lead frame  20 . In the embodiment shown, side rail  24  also servers as a dambar.  
         [0026]    [0026]FIG. 5 is a top plan view of the dual die package  100  of FIG. 2. The structure of second lead frame  40  for an LOC package is identical to first lead frame  20 , except that outer leads  49  are formed outside of second connection portions  45 . That is, outer leads  49  extend away from the second connection portions  45 . A dambar  46  is formed between outer leads  49 . Both ends of dambar  46  are connected to a side rail  44  of second lead frame  40 .  
         [0027]    First lead frame  20  having first chip  10  attached thereto is stacked on second lead frame  40  having second chip  30  attached thereto so that the back surface of first chip  10  is facing the back surface of second chip  30 . Adhesive layer  54  is interposed between side rail  24  of first lead frame  20  and side rail  44  of second lead frame  40  and mechanically connects first lead frame  20  to second lead frame  40 . Adhesive layer  54  can be formed on side rail  24  of first lead frame  20  and/or side rail  44  of second lead frame  40 . In the embodiment shown, adhesive layer  54  is formed on side rail  24  of first lead frame  20 . A liquid adhesive or a double-sided adhesive tape can be used for adhesive layer  54 .  
         [0028]    After the encapsulating step, side rails  24  and  44  are cut and removed by a trimming/forming step. At this time, first connection portions  25  may or may not be in contact with respective second connection portions  45 .  
         [0029]    Connection pads  27  are formed on first connection portions  25 . This allows first connection portions  25  to be electrically connected to second connection portions  45  via third bonding wires  66 . Connection pads  27  have a predetermined shape and protrude from the side surface of corresponding first connection portions  25 . Second connection portions  45  are electrically connected to corresponding connection pads  27  of corresponding first connection portion  25  via third bonding wires  66 . In this embodiment, third bonding wires  66  are connected to corresponding connection pads  27  via the ball bonding method and are connected to corresponding second connection portions  45  via the stitch bonding method. In some embodiments, connection pads  27  and second connection portions  45  are plated with silver (Ag), thereby providing excellent bondability with third bonding wires  66 . Although bonding wires  66  are connected to connection pads  27  via the ball bonding method and connected to second connection portion  45  via the stitch bonding method in the embodiment shown, those of ordinary skill in the art will recognize that these connection methods may be achieved in the reverse direction, or that the bonding wires may be connected to the second connection portion by the wedge bonding method.  
         [0030]    First lead frame  20  and second lead frame  40  are attached to one another by adhesive layer  54 , and first leads  21  and second leads  41  are electrically connected to one another via third bonding wires  66 . As a result, dual die package  100  of the present invention does not require a thermocompression process to be used to mechanically and electrically connect first leads  21  to second leads  41  and thus dual die package  100  of the present invention can be manufactured by using the conventional manufacturing equipment (e.g., conventional wire bonding equipment).  
         [0031]    As shown in FIG. 3, first chip  10 , second chip  30  and electrical connection parts including first, second and third bonding wires  62 ,  64  and  66  are encapsulated, thereby forming package body  80 . Outer leads  49  of second leads  41  extrude from package body  80  and are bent in a predetermined manner so that they can be mounted and serve as external connection terminals. In some embodiments, outer leads  49  are bent to form a gull wing shape.  
         [0032]    One advantage of the present invention is that first lead frame  20  is fixed to second lead frame  30  by adhesive layer  54 , which is advantageous because it provides stability during subsequent manufacturing steps.  
         [0033]    Another advantage of the present invention is that a thermocompression process is not required to attach first leads  21  and second leads  41 . Rather, first leads  21  and second leads  41  are electrically connected via third bonding wires  66  using conventional wire bonding equipment and are mechanically connected by adhesive layer  54 . Therefore, the present invention does not require non-conventional manufacturing equipment and thus reduces production costs for dual die packages.  
         [0034]    Moreover, compared to the conventional thermocompression process that connects the first leads of the first lead frame to the second leads of the second lead frame, it is easier to connect the first leads to the second leads using the wire bonding process and the resulting electrical connection between the first leads and the second leads is a more reliable.  
         [0035]    While particular embodiments of the present invention have been shown and described, it will be apparent to those skilled in the art that changes and modifications may be made without departing from this invention in its broader aspect and, therefore, the appended claims are to encompass within their scope all such changes and modifications as fall within the true spirit of this invention.