Abstract:
A semiconductor device includes a wiring board, a semiconductor chip mounted on the wiring board, the semiconductor chip including a bump formation surface, a plurality of first bumps provided within a first region of the bump formation surface, the first bumps being arranged in a first area density, a plurality of second bumps provided within a second region of the bump formation surface, the second bumps being arranged in a second area density, and a plurality of third bumps arranged between the first region and the second region of the bump formation surface in a two-dimensional array. The plurality of third bumps are arranged in a third area density being higher than the second area density and being lower than the first area density.

Description:
INCORPORATION BY REFERENCE 
       [0001]    The present application is a Continuation application of U.S. patent application Ser. No. 12/588,394, filed on Oct. 14, 2009, which is based and claims priority from Japanese Patent Application No. JP 2008-293191, filed on Nov. 17, 2008, the entire contents of which is incorporated herein by reference. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to a semiconductor device and a method of manufacturing the semiconductor device. 
         [0004]    2. Description of the Related Art 
         [0005]    A semiconductor package (a semiconductor device) includes a semiconductor chip and a wiring board on which the semiconductor chip is mounted. The semiconductor chip is provided with a bump formation surface on which protruding bumps are formed. Solder, for example, is used as a material for the bumps. The semiconductor chip is mounted on the wiring board by using the bump formation surface. 
         [0006]    In such a semiconductor device, stress is applied to the semiconductor chip and the bumps at the time of mounting the semiconductor chip or after the mounting in some cases. For example, in a case where flux is used to form the bumps, the semiconductor chip is mounted on the wiring substrate by a heat treatment such as an IR reflow treatment. In this mounting, stress sometimes occurs due to such reason as a difference in thermal expansion coefficient between the bump portions and the other portions. Such stress may cause a bump crack or a chip crack. Thus, reduction of such stress is desired. 
         [0007]    As a related art, Japanese Patent Application Publication No. 2007-242782 discloses a technique relating to a semiconductor device in which bumps serving as external connecting terminals are joined to a semiconductor substrate. An object of this technique is to reduce or absorb stress which the bumps receive from a mounting board and at the same time ensure stable electrical connection. 
         [0008]    Another related art is Japanese Patent Application Publication No. 2007-142017. This patent document discloses that bumps between a chip and a wiring board are arranged in concentric circles, and have diameters changing from the center circle toward the outermost circle in order to disperse stress occurring in the circumferential portion of the chip. 
         [0009]    In some cases, stress occurring in a bump formation surface of a semiconductor chip notably increases due to a difference in the density of bumps arranged on the bump formation surface. 
         [0010]      FIG. 1  is a schematic view, showing an example of an arrangement of bumps  101  on a bump formation surface  102 . In the example shown in  FIG. 1 , the bumps  101  are uniformly arranged. In this case, there is no difference in the density of the bumps, and thus stress relating to the density of the bumps occurs less. 
         [0011]      FIG. 2  is a schematic view showing another example of an arrangement of the bumps  101  on the bump formation surface  102 . In the example shown in  FIG. 2 , the bump formation surface  102  includes a first region  103  in which the bumps  101  are densely arranged and a second region  104  in which the bumps  101  are sparsely arranged.  FIG. 3  shows a simulation result of a stress distribution which occurs at the time of mounting a semiconductor chip and after the mounting. The simulation result in  FIG. 3  is obtained by use of a semiconductor chip having the bump formation surface  102  shown in  FIG. 2 . As shown in  FIG. 3 , stress occurring portions  105  occur around a border between the first region  103  and the second region  104 . 
         [0012]    Apparently, there is a problem that stress at a problematic level for a product occurs when the arrangement of the bumps  101  has a notable density difference as shown in  FIG. 3 . 
       SUMMARY 
       [0013]    A semiconductor device according to the present invention includes: a wiring board ( 1 ); and a semiconductor chip which includes a bump formation surface ( 7 ) having a bump group ( 3 ) formed thereon and which is mounted on the wiring board ( 1 ) by using the bump group ( 3 ). The bump formation surface ( 7 ) includes: a first region ( 9 ) in which an area density of a region having bumps ( 3 ) arranged therein is a first density; a second region ( 10 ) in which an area density of a region having bumps ( 3 ) arranged therein is a second density lower than the first density; and a third region ( 11 ) provided in a border portion between the first region ( 9 ) and the second region ( 10 ). In the third region ( 11 ), an area density of a region having bumps ( 3 ) arranged therein is higher than the second density and is lower than the first density. 
         [0014]    According to the present invention, stress occurring between the first region ( 9 ) and the second region ( 10 ) due to a difference in the density of the bumps is reduced by providing the third region ( 11 ). Thus, a bump crack and a chip crack due to the stress can be suppressed. 
         [0015]    A semiconductor chip according to the present invention includes a bump formation surface ( 7 ) which faces a wiring board ( 1 ) when mounted on the wiring board ( 1 ) and which has a bump group ( 3 ) formed thereon, the bump group ( 3 ) electrically connected to the wiring board ( 1 ). In the semiconductor chip, the bump formation surface ( 7 ) includes: a first region ( 9 ) in which an area density of a region having bumps ( 3 ) arranged therein is a first density; a second region ( 10 ) in which an area density of a region having bumps ( 3 ) arranged therein is a second density lower than the first density; and a third region ( 11 ) for reducing stress occurring at the time of mounting the semiconductor chip on the wiring board ( 1 ). The third region ( 11 ) is provided in a border portion between the first region ( 9 ) and the second region ( 10 ). In the third region ( 11 ), an area density of a region having bumps ( 3 ) arranged therein is higher than the second density and is lower than the first density. 
         [0016]    A wiring board according to the present invention includes a chip mounting surface ( 12 ) on which a semiconductor chip is to be mounted. Electrode terminals ( 5 ) are arranged on the chip mounting surface ( 12 ) in a pattern corresponding to the bump formation surface ( 7 ) of the semiconductor chip described above. 
         [0017]    A method of manufacturing a semiconductor device according to the present invention includes the steps of: preparing a wiring board ( 1 ) including an electrode terminal group ( 5 ); preparing a semiconductor chip including a bump formation surface ( 7 ) which has a bump group ( 3 ) formed thereon, the bump formation surface ( 3 ) including a first region ( 9 ) in which an area density of a region having bumps ( 3 ) arranged therein is a first density, a second region ( 10 ) in which an area density of a region having bumps ( 3 ) arranged therein is a second density lower than the first density, and a third region ( 11 ) which is for reducing stress occurring at the time of mounting the semiconductor chip on the wiring board ( 1 ), which is provided in a border portion between the first region ( 9 ) and the second region ( 10 ), and in which an area density of a region having bumps ( 3 ) arranged therein is higher than the second density and is lower than the first density; and mounting the semiconductor chip on the wiring board ( 1 ) by heat treatment so that the bump group ( 3 ) faces the electrode terminal group ( 5 ). 
         [0018]    The present invention provides a semiconductor device capable of reducing stress even when an arrangement of bumps has a density difference, and a method of manufacturing such a semiconductor device. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0019]      FIG. 1  is a schematic view showing an example of an arrangement of bumps on a bump formation surface. 
           [0020]      FIG. 2  is a schematic view showing another example of the arrangement of the bumps on the bump formation surface. 
           [0021]      FIG. 3  is a simulation result of a stress distribution. 
           [0022]      FIG. 4  is a cross-sectional view showing a semiconductor device according to a first embodiment. 
           [0023]      FIG. 5  is a schematic view showing an arrangement of bumps in a part of a bump formation surface. 
           [0024]      FIG. 6  is a simulation result of a stress distribution in the first embodiment. 
           [0025]      FIG. 7  is a simulation result of the amount of stress. 
           [0026]      FIG. 8  is a schematic view showing a bump formation surface of a semiconductor device according to a second embodiment. 
           [0027]      FIG. 9  is a simulation result which shows a relation between bump size and stress. 
           [0028]      FIG. 10  is a schematic view showing a bump formation surface of a semiconductor device according to a third embodiment. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     First Embodiment 
       [0029]    A first embodiment according to the present invention will be described with reference to the drawings.  FIG. 4  is a cross-sectional view showing a semiconductor device according to the present embodiment. 
         [0030]    As shown in  FIG. 4 , the semiconductor device of the present embodiment includes a wiring board and a semiconductor chip  13 . The wiring board  1  has a chip mounting surface  12 . On the chip mounting surface  12 , multiple electrode terminals  5  are formed as an electrode terminal group. Meanwhile, the semiconductor chip  13  includes a chip substrate  2  having a semiconductor integrated circuit formed thereon. The chip substrate  2  is provided with a bump formation surface  7 . Multiple bumps  3  are formed on the bump formation surface  7  as a bump  3  group. The semiconductor chip  13  is mounted on the wiring board  1  so that the bump formation surface  7  would face the chip mounting surface  12 . An arrangement pattern of the bumps  3  on the bump formation surface  7  is the same as an arrangement pattern of the electrode terminals  5  on the chip mounting surface  12 . The bumps  3  and the electrode terminals  5  are electrically connected to each other. Moreover, a space between the semiconductor chip  13  and the wiring board  1  is sealed with sealing resin  4 . Connecting parts between the semiconductor chip  13  and the wiring substrate  1  are protected by the sealing resin  4 . 
         [0031]    As shown in  FIG. 4 , the semiconductor device according to the present embodiment is a so-called flip-chip semiconductor package. 
         [0032]      FIG. 5  is a schematic view showing the arrangement of the bumps in a part of the bump formation surface  7 . As shown in  FIG. 5 , the bump formation surface  7  includes a first region  9 , a second region  10 , and a third region  11 . 
         [0033]    In the first region  9 , the area density of a region having the bumps  3  arranged thereon is a first density. 
         [0034]    In the second region  10 , the area density of a region having the bumps  3  arranged thereon is a second density. The second density is lower than the first density. 
         [0035]    The third region  11  is provided to suppress stress occurring due to a difference in densities of the bumps  3  between the first region  9  and the second region  10 . The third region  11  is located in a border portion between the first region  9  and the second region  10 . In the third region  11 , the area density of a region having the bumps  3  arranged thereon is a third density. The third density is higher than the second density, and is lower than the first density. In other words, the area density increases in the regions having the bumps  3  arranged thereon in the order of the first region  9 , the third region  11 , and the second region  10 . 
         [0036]    Note that, the area density is the proportion, in a predetermined region, of the area of a portion where the bumps are arranged to the sum of the area of the portion where the bumps are arranged and the area of a portion where no bumps are arranged. 
         [0037]    Moreover, the bumps  3  in the first region  9 , the second region  10 , and the third region  11  all have the same size. In other words, the first region  9 , the second region  10 , and the third region  11  have different numbers of the bumps  3  per unit area. Accordingly, the area densities of the respective regions having the bumps arranged thereon are different from each other. In each of the first region  9 , the second region  10 , and the third region  11 , the bump  3  are arranged at almost equal intervals. 
         [0038]    To manufacture a semiconductor device such as one described above, firstly, the semiconductor chip  13  and the wiring substrate  1  are prepared. In the preparation of the semiconductor chip  13 , the bumps  3  are formed by using flux. Thereafter, the semiconductor chip  13  is mounted on the wiring board  1 . At this time, a heat treatment such as an IR reflow treatment is performed. 
         [0039]    In the heat treatment, stress is likely to occur due to a difference in thermal expansion coefficients between portions corresponding to the bump  3  and the other portions. However, in the present embodiment, the third region  11  is provided in the border portion between the first region  9  and the second region  10  as shown in  FIG. 5 . Thus, the density of the bumps  3  in the bump formation surface  7  changes stepwisely. By this arrangement, the portion where the density of the bumps  3  suddenly changes is eliminated, thereby reducing the stress. As a result a bump crack and a chip crack are suppressed. 
         [0040]      FIG. 6  shows a simulation result of a stress distribution occurring in the present embodiment. Stress occurring portions  8  occur in a border portion between the first region  9  and the third region  11  and in a border portion between the third region  11  and the second region  10 . The stress occurring portions  8  are dispersed compared to a case where the third region  11  is not provided (see  FIG. 3 ). 
         [0041]      FIG. 7  shows a simulation result of the amount of stress. In  FIG. 7 , the vertical axis indicates the amount of stress, and the horizontal axis indicates the present embodiment (the first embodiment) and Comparative Example 1. Comparative Example 1 is an example in which the region corresponding to the third region  11  is replaced with the second region. In  FIG. 7 , a white circle for the first embodiment indicates stress in the border portion between the first region  9  and the third region  11 , and a black circle for the first embodiment indicates stress in the border portion between the third region  11  and the second region  10 . As to Comparative Example 1, a white circle and a black circle each indicate stress in a portion corresponding to the portion indicated for the present embodiment. 
         [0042]    As shown in  FIG. 7 , the amount of the stress is reduced in the present embodiment compared to Comparative Example 1 in both the border portion between the first region  9  and the third region  11  and the border portion between the third region  11  and the second region  10 . The fact that the stress is reduced by providing the third region  11  is confirmed from the simulation result. 
         [0043]    In the present embodiment, the case where the semiconductor chip  13  is flip-chip mounted on the wiring substrate  1  is described. However, the present invention is not limited to this, and it should be understood that the present invention can be applied to any case where a semiconductor chip is mounted on a chip, a substrate or the like by using bumps. 
       Second Embodiment 
       [0044]    Next, a second embodiment will be described.  FIG. 8  shows a bump formation surface  7  of a semiconductor device according to the second embodiment. In the present embodiment, the size and the arrangement of bumps  3  in a third region  11  are different from those in the first embodiment. The other points may be the same as the first embodiment, and thus the detailed description thereof is omitted here. 
         [0045]    In the present embodiment, as in the case of the first embodiment, the region of the third region  11  having the bumps  3  arranged thereon has an area density (third density) which is higher than a second density and is lower than a first density. However, in the present embodiment, the number of the bumps  3  arranged per unit area in the third region  11  is the same as that in the second region  10 . Meanwhile, the size of each of the bumps  3  arranged in the third region  11  is larger than the size of each of the bumps  3  arranged in the first region  9  and the second region  10 . Note that, the bumps  3  in the first region  9  and the bumps  3  in the second region  10  are all the same in size. 
         [0046]    In other words, in the present embodiment, the bumps  3  of the third region  11  and the bumps  3  of the second region  10  are different in size. Thus, the density of the bumps in the bump formation surface  7  changes stepwisely. 
         [0047]    In the present embodiment, stress can also be reduced, and a bump crack and a chip crack can be suppressed, as in the case of the first embodiment. 
         [0048]      FIG. 9  is a simulation result which shows a relation between the bump size in the third region  11  and stress. In  FIG. 9 , the horizontal axis indicates the size of each of the bumps  3  arranged in the third region  11 , and the vertical axis indicates the amount of stress. Moreover, as in the case of the first embodiment, each of white circles indicates stress in the border, portion between the first region  9  and the third region  11 , and each of black circles indicates stress in the border portion between the third region  11  and the second region  10 . The bump size is 1.00 in the first region  9  and the second region  10 . The number of the bumps per unit area in the third region  11  is the same as that in the second region  10 . 
         [0049]    As shown in  FIG. 9 , the amount of stress is the smallest when the bump size in the third region  11  is set at 1.15, and is the largest when the bump size in the third region  11  is set at 0.85. Thus, the fact that the stress is reduced by increasing the bump size in the third region  11  is confirmed. 
       Third Embodiment 
       [0050]    Next, a third embodiment of the present invention will be described.  FIG. 10  shows a bump formation surface  7  of a semiconductor device according to the third embodiment. In the present embodiment, a bump group provided on the bump formation surface  7  includes actual bumps  3 - 1  and dummy bumps  3 - 2 . The other points maybe the same as the above-described embodiments, and thus the detailed description thereof is omitted here. 
         [0051]    The actual bumps  3 - 1  are bumps used for electrical connection between a semiconductor chip  13  and a wiring board  1 . On the other hand, the dummy bumps  3 - 2  are provided to control the area density of a region where the bumps are arranged, and are not used for the electrical connection between the semiconductor chip  13  and the wiring board  1 . 
         [0052]    According to the present embodiment, the stress can be reduced by the same effects as the above-described embodiments. In addition, the area density of a region where the bumps  3  are arranged can be controlled by the dummy bumps  3 - 2 . Accordingly, the present embodiment is advantageous in that a layout of the bumps  3  is less restricted. 
         [0053]    Although the inventions has been described above in connection with several preferred embodiments thereof, it will be appreciated by those skilled in the art that those embodiments are provided solely for illustrating the invention, and should not be relied upon to construe be appended claims in a limiting sense.