Abstract:
A package structure includes a substrate, a first die and at least one second die. The substrate includes a first pair of parallel edges and a second pair of parallel edges. The first die is mounted over the substrate. The first die includes a third pair of parallel edges and a fourth pair of parallel edges, wherein the third pair of parallel edges and the fourth pair of parallel edges are not parallel to the first pair of parallel edges and the second pair of parallel edges, respectively. The at least one second die is mounted over the first die.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to semiconductor structures, and more particularly to package structures. 
         [0003]    2. Description of the Related Art 
         [0004]    With advances associated with electronic products, semiconductor technology has been widely applied in manufacturing memories, central processing units (CPUs), liquid crystal displays (LCDs), light emission diodes (LEDs), laser diodes and other devices or chipsets. In order to achieve high-integration and high-speed goals, dimensions of semiconductor integrated circuits continue to shrink. In addition, various package techniques also have been proposed or provided to improve performances of integrated circuits. 
         [0005]      FIG. 1A  is a top view of a prior art package structure. 
         [0006]    Referring to  FIG. 1A , a die  110  is mounted over a printed circuit board (PCB)  100 . The PCB  100  and the die  110  have square shapes. The PCB  100  has two pairs of parallel edges  101  and  103 . The die  110  has two pairs of parallel edges  111  and  113 . A plurality of bumps (not shown) are formed over the die  110  for connecting with other die or substrate (not shown). The edges  111  and  113  are parallel to the edges  101  and  103 , respectively. In addition, corners  105  of the PCB  100  are aligned with corners  115  of the die  110  along the diagonal direction b 1 . 
         [0007]    By using the package structure shown in  FIG. 1A , circuits formed over the die  110  are electrically coupled to electrical routings defined over the PCB  100  via a plurality of bumps (not shown). Accordingly, signals generated from the circuits of the die  110  can be transmitted to the PCB  100  and then to another substrate or PCB (not shown) which is electrically coupled to the PCB  100 . However, it is found that the bumps (not shown) formed between the die  110  and the substrate  100  are vulnerable to delamination during reliability tests and may be detached from the package structure during and/or after the reliability tests. The detachment of bumps is generally referred to as “white bumps.” 
         [0008]      FIG. 1B  is a top view of another prior art package structure. 
         [0009]    Referring to  FIG. 1B , static random access memories (SRAMs)  130  are mounted at corner regions of a printed circuit board (PCB)  120 . A central processing unit (CPU)  140  is mounted at the central region of the PCB  120 . The PCB  120 , the SRAMs  130  and the CPU  140  have square shapes. The PCB  120  has two pairs of parallel edges  121  and  123 . The SRAMs  130  and the CPU  140  have two pairs of parallel edges  131 ,  133  and  141 ,  143 , respectively. A plurality of bumps (not shown) are formed between the SRAMs  130  and the PCB  120 , and between the CPU  140  and the PCB  120  for connecting with another die or substrate (not shown). The edges  131  and  133  are parallel to the edges  121  and  123 , respectively. In addition, corners  125  of the PCB  120  are aligned with corners  135  of the die  130  along the diagonal direction. 
         [0010]    By the package structure shown in  FIG. 1B , circuits formed over the SRAMs  130  and the CPU  140  are electrically coupled to routings defined over the PCB  120 . In other words, signals generated from the circuits of the SRAMs  130  and the CPU  140  can be transmitted to the PCB  120  and then to another substrate or PCB (not shown) which is electrically coupled to the PCB  120 . The package structure, in which the CPU  140  is rotated and disposed at the center of the PCB  120  has a dimension smaller than that of a structure in which a CPU has edges parallel to edges of the SRAMs  130 . However, it is found that the bumps (not shown) formed between the SRAMs  130  and the PCB  120 , and/or between the CPU  140  and the PCB  120  are vulnerable to delamination during reliability tests and may be detached from the package structure. 
         [0011]    From the foregoing, new package structures are desired. 
       SUMMARY OF THE INVENTION 
       [0012]    In accordance with some exemplary embodiments, a package structure comprises a substrate, a first die and at least one second die. The substrate includes a first pair of parallel edges and a second pair of parallel edges. The first die is mounted over the substrate. The first die includes a third pair of parallel edges and a fourth pair of parallel edges, wherein the third pair of parallel edges and the fourth pair of parallel edges are not parallel to the first pair of parallel edges and the second pair of parallel edges, respectively. The at least one second die is mounted over the first die. 
         [0013]    The above and other features will be better understood from the following detailed description of the preferred embodiments of the invention that is provided in connection with the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0014]    Following are brief descriptions of exemplary drawings. They are mere exemplary embodiments and the scope of the present invention should not be limited thereto. 
           [0015]      FIGS. 1A-1B  are top views of prior art package structures. 
           [0016]      FIG. 2A  is a schematic top view of an exemplary package structure. 
           [0017]      FIGS. 2B and 2D  are simulation results regarding stresses of the die  110  mounted over the traditional package structure shown in  FIG. 1  along directions a 1  and b 1 , and  FIGS. 2C and 2E  are simulation results regarding stresses of the die  210  mounted over the exemplary package structure shown in  FIG. 2A  along directions a 2  and b 2 , respectively. 
           [0018]      FIG. 3  is a top view showing another exemplary package structure. 
           [0019]      FIG. 4A  is a top view showing an exemplary package structure. 
           [0020]      FIG. 4B  is a top view showing another exemplary package structure. 
           [0021]      FIG. 4C  is a top view showing an exemplary package structure. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0022]    This description of the exemplary embodiments is intended to be read in connection with the accompanying drawings, which are to be considered part of the entire written description. In the description, relative terms such as “lower,” “upper,” “horizontal,” “vertical,” “above,” “below,” “up,” “down,” “top” and “bottom” as well as derivatives thereof (e.g., “horizontally,” “downwardly,” “upwardly,” etc.) should be construed to refer to the orientation as then described or as shown in the drawing under discussion. These relative terms are for convenience of description and do not require that the apparatus be constructed or operated in a particular orientation. 
         [0023]      FIG. 2A  is a schematic top view of an exemplary package structure. 
         [0024]    Referring to  FIG. 2A , a single die  210  is mounted over a substrate  200 . The substrate  200  may comprise two pairs of parallel edges  201  and  203 . The single die  210  may comprise two pairs of parallel edges  211  and  213 . The parallel edges  211  and  213  are not parallel to the parallel edges  201  and  203 . The substrate  200  may comprise a plurality of corners  205  and the single die  210  may comprise a plurality of corners  215 . In some embodiments, the corners  205  of the substrate  200  are not aligned with the corners  215  of the single die  210 . That is, a diagonal passing through the corners  205  of substrate  200  does not pass through the corners  215  of the die  210 . 
         [0025]    The substrate  200  can be a printed circuit board (PCB), plastic substrate, ceramic substrate, silicon substrate, III-V compound substrate, display substrate such as a liquid crystal display (LCD), plasma display, electro luminescence (EL) lamp display, or light emitting diode (LED) substrate (collectively referred to as, substrate  200 ), for example. In some embodiments, the substrate  200  may comprise a plurality of ball grid arrays (BGAs) (not shown) disposed over the surface of the substrate  200  opposite to the surface over which the die  210  is mounted. 
         [0026]    The single die  210  can be, for example, a silicon substrate, III-V compound substrate, display substrate such as a liquid crystal display (LCD), plasma display, electro luminescence (EL) lamp display, or light emitting diode (LED) substrate over which a plurality of devices, diodes, transistors and/or circuits are formed. The single die  210  may be wire bonded and/or flip-chip mounted over the substrate  200 . The package structure formed by a flip-chip process is generally referred to as a flip-chip ball grid array (FCBGA) package. In other words, the FCBGA package includes a plurality of bumps (not shown) between the substrate  200  and the single die  210 . In some embodiments, the substrate  200  and the die  210  have different thermal expansion coefficients from each other. 
         [0027]      FIGS. 2B and 2D  are simulation results regarding stresses of the die  110  mounted over the traditional package structure as shown in  FIG. 1  along directions a 1  and b 2 , and  FIGS. 2C and 2E  are simulation results regarding stresses of the die  210  mounted over the exemplary package structure shown in  FIG. 2A  along directions a 2  and b 2 , respectively. 
         [0028]    It is found that due to the difference of coefficients of thermal expansion (CTE) of the substrate  200  and the die  210 , the die  210  and the substrate  200  are subjected to different stresses (e.g., expansion vs. compression) after the die  210  is mounted over the substrate  200 . 
         [0029]    Referring to  FIGS. 2B and 2C , the die  110  mounted over the substrate  100  is subjected to a maximum stress of about 124 MPa at the edge  111  in the direction a 1 . The die  210  mounted over the substrate  200  is subjected to a maximum stress of about 81.5 MPa at the central region of the die  210  in the direction b 2 . Also as shown in  FIGS. 2C and 2E , the die  110  is subjected to a maximum stress of about 107 MPa at the central region of the die  110  in the direction b 1 , and the die  210  is subjected to a maximum stress of about 80.3 MPa at the regions near to the corners  215  and the central region in the direction a 2 . 
         [0030]    Based on the simulation results, it is preferred that the edges  211  and  213  of the die  210  are not parallel to the edges  201  and  203  of the substrate  200 . In addition, it is preferred that the corners  215  of the die  210  are not aligned with the corners  205  of the substrate  200  in diagonal direction. By the disposition of the die  210  over the substrate  200  in a non-aligned configuration, as shown in  FIG. 2A , stresses at the centers, edges  211 ,  213  and/or corners  215  of the die  210  can be desirably reduced. 
         [0031]    In some embodiments, a dimension d 1  of at least one of the pairs of parallel edges  201  and  203  of the substrate  200  is about 42 millimeters (mm) or more and a dimension d 2  of at least one of the pairs of parallel edges  211  and  213  of the die  210  is about 20 mm or more. In other embodiments, the substrate  200  has a size of about 42×42 mm 2  and the die has a die size of about 20×20 mm 2 . In still other embodiments, at least one of the substrate  200  and the die  210  has a rectangular shape. It will be understood that in the case where one of the substrate and the die has a square shape and the other of the substrate and the die has a non-square, rectangular shape, the die and the substrate are considered aligned if the edges of the die are parallel to respective edges of the substrate, and are considered non-aligned if none of the edges of the die are parallel to the edges of the substrate. 
         [0032]    In some embodiments, one of the parallel edges  201  and  203  of the substrate  200  and one of the parallel edges  211  and  213  of the die  210  form an angle θ between about 15° and about 45° therebetween. 
         [0033]    The single die  210  is mounted over the substrate  200  such that a desired area ratio of the single die  210  to the substrate  200  can be achieved. The desired area ratio can be about 0.1 or less such that a difference of CTE between the die  210  and the substrate  200  does not generate excessive stresses on the die  210  and/or the substrate  200 . If a big die  210  is mounted over a small substrate  200 , stresses of the die  210  will increase and may cause white bumps during and/or after reliability tests. 
         [0034]      FIG. 3  is a top view showing another exemplary package structure. 
         [0035]    Referring to  FIG. 3 , a substrate  300  may comprise pairs of parallel edges  301  and  303 , wherein the substrate  300  may comprise at least one corner region  307  and at least one central region  309 . At least one die  320  is mounted at the central region  309  of the substrate  300 . The die  320  may comprise pairs of parallel edges  321  and  323 . At least one die  310  is mounted at the corner region  307  of the substrate  300 . The die  310  may comprise pairs of parallel edges  311  and  313 , wherein the parallel edges  311  and  313  of the die  310  are not parallel to the parallel edges  301  and  303  of the substrate  300 , respectively. In addition, the die  310  may comprise a plurality of corners  315  and the substrate  300  may comprise a plurality of corners  305 . In other embodiments, the corners  315  of the die  310  are not aligned with the corners  305  of the substrate  300 . 
         [0036]    The substrate  300  and the dies  310 ,  320  are similar to the substrate  200  and the die  210 , respectively, set forth above in connection with  FIG. 2A . It is found that the difference of coefficients of thermal expansion of the substrate  300  and the dies  310 ,  320  are more serious at the corner region  307  of the substrate  300  than at the central region  309  of the substrate  300 . The disposition of the dies  310  whose pairs of parallel edges  311  and  313  are not parallel to the edges  301  and  303  of the substrate  300  can desirably reduce stresses of the dies  310  at the corner regions  307  of the substrate  300 . In other embodiments, the disposition of the dies  310  such that the corners  315  of the dies  310  are not aligned with the corners  305  of the substrate  300  can desirably reduce the stresses of the dies  310 , too. 
         [0037]    In some embodiments, the edges  321 ,  323  of the die  320  are not parallel to the edges  301 ,  303  of the substrate  300 , respectively, such that desired reduction in stresses of the die  320  can also be achieved. In other embodiments, the corners  325  of the die  320  are not aligned with the corners of the substrate  300  in the diagonal direction. 
         [0038]      FIG. 4A  is a top view showing an exemplary package structure. 
         [0039]    Referring to  FIG. 4A , at least one die  420  is mounted over the die  210 . The package structure shown in  FIG. 4A  is generally referred to as a stacked-module package (SMP). The die  420  may be similar to the die  210  set forth above in connection with  FIG. 2A . The die  420  may comprise pairs of parallel edges  421  and  423 . In some embodiments, the parallel edges  421  and  423  of the die  420  are not parallel to the parallel edges  211  and  213  of the die  210 . Further, in some embodiments, one of the parallel edges  421 ,  423  of the die  420  and one of the parallel edges  211 ,  213  of the substrate  200  form an angle ( ) between about 15° and about 45°. 
         [0040]    In some embodiments, the corners  425  of the die  420  are not aligned with the corners  215  of the die  210 . In other embodiments, the edges  421 ,  423  of the die  420  are parallel to the edges  201 ,  203  of the substrate  200 , respectively. In still other embodiments, the corners  425  of the die  420  are aligned with the corners  205  of the substrate in the diagonal direction. 
         [0041]      FIG. 4B  is a top view showing another exemplary package structure. 
         [0042]    Referring to  FIG. 4B , a die  430  is mounted over the die  210 . The die  430  may be similar to the die  210  described above in connection with  FIG. 2B . In the embodiment of  FIG. 4B , the die  430  may comprise pairs of parallel edges  431  and  433 , which are parallel to the parallel edges  211  and  213 , respectively. In some embodiments, the corners  435  of the die  430  are not aligned with the corners  205  of the substrate  200 . This disposition of the die  430  over the die  210  is desirable if stresses of the die  430  and/or  210  would not destroy the package structure during and/or after reliability tests. 
         [0043]      FIG. 4C  is a top view showing an exemplary package structure. 
         [0044]    Referring to  FIG. 4C , at least one die  440  is mounted over a substrate  400 , and at least one die  450  is mounted over the die  440 . The substrate  400  and dies  440  and  450  may be similar to the substrate  200  and the die  210 , respectively, described above in connection with  FIG. 2A . The substrate  400  may comprise pairs of parallel edges  401  and  403 , the die  440  may comprise pairs of parallel edges  441  and  443 , and the die  450  may comprise pairs of parallel edges  451  and  453 . In some embodiments, the edges  451  and  453  are not parallel to the edges  441  and  443 . In some embodiments, one of the parallel edges  451 ,  453  of the die  450  and one of the parallel edges  441 ,  443  of the die  440  form an angle θ between about 15° and about 45°. In some embodiments, the edges  441  and  443  of the die  440  are parallel to the edges  401  and  403  of the substrate  400 , respectively, if stresses of the substrate  400  and the die  440  are desired. 
         [0045]    In some embodiments, the edges  451 ,  453  of the die  450  are not parallel to the edges  401 ,  403  of the substrate  400 , respectively. In some embodiments, the corners  455  of the die  450  are not aligned with the corners  405  of the substrate  400 . 
         [0046]    Although the present invention has been described in terms of exemplary embodiments, it is not limited thereto. Rather, the appended claims should be construed broadly to include other variants and embodiments of the invention which may be made by those skilled in the field of this art without departing from the scope and range of equivalents of the invention.