Abstract:
A semiconductor device having a wafer level chip size package may include a semiconductor substrate having an integrated circuit formed thereon; a plurality of electrode pads formed on the semiconductor substrate; at least one rewiring layer which may include rewiring formed adjacent to the plurality of electrode pads; and a plurality of external electrodes formed on the rewiring layer. The plurality of electrodes and plurality of external electrodes may be sectioned and arranged in four areas having the same shapes. Each area may include a first group of N number of external electrodes arranged along an edge of the semiconductor substrate, a second group of (N−2) number of external electrodes arranged inside the first group of external electrodes, and a plurality of (2N−2) number of electrode pads arranged between the first and second groups of external electrodes.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a continuation application of the U.S. patent application Ser. No. 11/238,189 filed Sep. 29, 2005, the contents of which are incorporated by reference herein in their entirety, priority to which is claimed under 35 U.S.C. § 120. U.S. application Ser. No. 11/238,189 claims the benefit of the date of the earlier filed Japanese Patent Application No. JP 2004-283167 filed on Sep. 29, 2004, the contents of which are incorporated herein by reference, and priority to which is also claimed herein. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The invention relates to a semiconductor device, and more particularly to a semiconductor device having a chip size package (hereinafter, referred to as CSP) structure. 
         [0004]    2. Description of the Related Art 
         [0005]    With the recent miniaturization of information terminals such as a cellular phone and a personal digital assistance (PDA), miniaturization of semiconductor devices to be used inside, such as LSIs, has been in increasing demand. Under such circumstances, attention has been given to a packaging technology called ball grid array (BGA) structure. 
         [0006]    Unlike conventional quad flat package (QFP) structures in which lead frames are used to connect semiconductor devices to a substrate, the BGA structure achieves substrate connection via terminals called solder bumps or solder balls which are formed on the surfaces of the semiconductor devices. According to this BGA structure, external connection terminals can be formed over the entire surfaces of semiconductor devices. This can eliminate the need for lead frames around the components, allowing a significant reduction in packaging area. 
         [0007]    By using this BGA structure, there has been developed a packaging technology called chip size package (CSP), in which the area of a semiconductor chip and the packaging area of the same are approximately equal. There has also been developed a technology called wafer level CSP (WL-CSP), in which solder bumps are formed directly on semiconductor chips without any substrate. This promotes the miniaturization of semiconductor devices (see Japanese Patent Laid-Open Publication No. 2003-297961). 
         [0008]    A semiconductor device to which this CSP technology is applied has external connection terminals made of solder bumps, which are often arranged systematically on the surface of the semiconductor device for the sake of connection with a printed-circuit board as shown in  FIG. 1  of the above-mentioned patent document. 
         [0009]    Meanwhile, given a semiconductor substrate having a semiconductor integrated circuit formed thereon, electrode pads intended for signal input and output are often arranged along the periphery of the semiconductor integrated circuit as is the case with the QFP structure. The electrode pads formed on the periphery of this semiconductor integrated circuit are routed by a rewiring layer to the positions of systematically-arranged solder bumps for the sake of electric connection. 
         [0010]    Under the circumstances, the inventor has become aware of the following problem.  FIG. 5  shows an example of the layout of electrode pads and solder bumps on a semiconductor device  500  having the CSP structure, showing the problem of the present invention. Electrode pads  10  are arranged along the periphery of the semiconductor device  500 . Solder bumps  20 , or external lead electrodes, are also arranged systematically on the semiconductor device  500 . Rewiring  30  routes signals from the positions of the electrode pads  10  to the positions of the solder bumps  20 , or external lead electrodes, for respective electric connections. As in  FIG. 1  of the patent document, the solder bumps  20  are arranged on this semiconductor device  500  inside the electrode pads  10 . 
         [0011]    Now, focus attention on the electrode pads  10   a  and  10   b , and the solder bumps  20   a  to  20   d . The electrode pads  10   a  and  10   b  are connected to the inner solder bumps  20   a  and  20   b , respectively, out of the solder bumps arranged in two rows. In this case, rewiring traces  30   a  and  30   b  must be laid so as to pass between the solder bumps  20   c  and  20   d.    
         [0012]    As a result, the rewiring traces  30   a  and  30   b  have greater lengths than that of a rewiring trace  30   c  to be connected with the outer solder bump  20   c . This causes differences in the rewiring length, which can adversely affect circuit characteristics including resistances and inductances. 
         [0013]    In order to lower these resistances and inductances, it might be desired to put the solder bumps  20  closer to the chip edges. Nevertheless, the distance between a chip edge and a solder bump  20 , designated by d in the diagram, is restricted by the rewiring. The reason is that the distances from the rewiring traces to the respective electrode pads and solder bumps must be rendered greater than a predetermined distance which is determined by design rules on the semiconductor manufacturing process of the semiconductor device  500 . For example, trying to put the solder bump  20   c  closer to the chip edge of the semiconductor device  500  has limitations since the rewiring trace  30   a  and the solder bump  20   c , and the rewiring trace  30   a  and the electrode pad  10   b , must be spaced wider than a certain distance determined by the design rules. 
         [0014]    Consequently, useless gaps required for the rewiring layout appear on the periphery of the semiconductor device  500  outside the solder bumps  20 . There has thus been the problem of an increased chip size. 
       SUMMARY OF THE INVENTION 
       [0015]    One of the aspects of the present invention relates to a semiconductor device. This semiconductor device comprises: a semiconductor substrate having an integrated circuit formed thereon; a plurality of electrode pads formed on the semiconductor substrate, being intended for input and output of signals between the integrated circuit and an external circuit; and a plurality of external electrodes connected to the plurality of electrode pads via rewiring, the external electrodes making connection terminals for the external circuit. The plurality of external electrodes include a first group of external electrodes arranged along an edge of the semiconductor substrate and a second group of external electrodes arranged inside the first group of external electrodes. The plurality of electrode pads are arranged between the first group of external electrodes and the second group of external electrodes, and are each connected to an external electrode included in either the first group of external electrodes or the second group of external electrodes via the rewiring. 
         [0016]    The “electrode pads intended for input and output of signals between the integrated circuit and the external circuit” refer to electrode pads that supply signals to, lead out signals from, or ground or otherwise treat the circuit elements constituting the integrated circuit. The “external electrodes” refer to electrodes that function as terminals for connecting to the external circuit, such solder bumps, solder balls, or posts. 
         [0017]    According to this aspect, the plurality of electrode pads are arranged between the first group of external electrodes and the second group of external electrodes. Consequently, the external electrodes included in either of the groups can be connected by approximately the same distances of rewiring. Since the lengths of the rewiring traces have an impact on the wiring resistances and inductances, it is possible to suppress variations in the electric characteristics. In addition, since the rewiring need not be routed outside the first group of external electrodes, it is possible to put the first group of external electrodes closer to the outer edges of the semiconductor device without constraints from the layout of the rewiring. This can suppress an increase in chip size. 
         [0018]    The integrated circuit may include: input/output circuits to be connected to the plurality of electrode pads, being arranged on an outermost periphery of the semiconductor device; and a functional circuit arranged near the center of the semiconductor substrate. The plurality of electrode pads may be arranged between the input/output circuits and the functional circuit. 
         [0019]    The “input/output circuits” refer to protective elements which are connected with the respective electrode pads and protect internal circuit elements, and circuits which have a predetermined circuit configuration and size, such as an input/output buffer. Since the input/output circuits are disposed to the space above the integrated circuit, appearing outside the electrode pads, it is possible to improve the use efficiency of space. This allows a further reduction in chip size. 
         [0020]    The plurality of electrode pads may have a minimum spacing generally equivalent to an integral multiple of the minimum spacing of the plurality of external electrodes. 
         [0021]    With twice the spacing in particular, two adjoining external electrodes out of the first group of external electrodes and two out of the second group of external electrodes are located near respective corresponding four electrode pads. This allows economic, efficient rewiring. 
         [0022]    The first and second groups of external electrodes may be arranged systematically at regular intervals. The systematic arrangement of the external electrodes facilitates determining the layout of the electrode pads and the rewiring. 
         [0023]    The semiconductor device may further include an insulating film formed over the electrode pads, the insulating film having openings at locations above the electrode pads. The rewiring may be formed on this insulating film. 
         [0024]    Another aspect of the present invention is also a semiconductor device. This semiconductor device comprises: a semiconductor substrate having an integrated circuit formed thereon; a plurality of electrode pads formed on the semiconductor substrate, being intended for input and output of signals between the integrated circuit and an external circuit; and a plurality of external electrodes connected to the plurality of electrode pads via rewiring, the external electrodes making connection terminals for the external circuit. The plurality of external electrodes include a first row of group of external electrodes arranged linearly, and a second row of group of external electrodes arranged linearly in parallel with the first row of group of external electrodes. Some of the plurality of electrode pads are located in an area interposed between the first and second rows of groups of external electrodes, and are each connected to one of the external electrodes in either the first or second row of group of external electrodes by means of the rewiring. 
         [0025]    According to this aspect, the electrode pads are located in the area interposed between the external electrodes which are arranged in two parallel rows. The connections to the two rows can thus be made by almost the same distances of rewiring. 
         [0026]    The plurality of electrode pads may be arranged linearly in parallel with the first and second rows of groups of external electrodes. Since the plurality of electrode pads are arranged linearly, the external electrodes and the electrode pads are situated in parallel with each other. This can simplify the rewiring connections. 
         [0027]    The first row of group of external electrodes, the second row of group of external electrodes, and the plurality of electrode pads may be arranged systematically at regular intervals. The systematic arrangement of these also results in systematic layout of the rewiring. The rewiring connections can thus be simplified further. 
         [0028]    The first or second row of group of external electrodes may have a minimum spacing generally equivalent to an integral multiple of the minimum spacing of the plurality of electrode pads. 
         [0029]    It is to be noted that any arbitrary combination or rearrangement of the above-described structural components and so forth are all effective as and encompassed by the present embodiments. 
         [0030]    Moreover, this summary of the invention does not necessarily describe all necessary features so that the invention may also be sub-combination of these described features. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0031]    Embodiments will now be described, by way of example only, with reference to the accompanying drawings which are meant to be exemplary, not limiting, and wherein like elements are numbered alike in several Figures, in which: 
           [0032]      FIG. 1  is a plan view of a semiconductor device according to a first embodiment; 
           [0033]      FIG. 2  is a sectional view taken along the line  2 - 2  of  FIG. 1 ; 
           [0034]      FIG. 3A to 3D  are plan views of the semiconductor device according to a second embodiment, showing part of the layout of electrode pads, solder bumps, and rewiring; 
           [0035]      FIGS. 4A and 4B  are plan views of part of the semiconductor device according to a third embodiment in a manufacturing phase; and 
           [0036]      FIG. 5  shows an example of the layout of electrode pads and solder bumps on a semiconductor device having a CSP structure, explaining the problem of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0037]    The invention will now be described based on preferred embodiments which do not intend to limit the scope of the present invention but exemplify the invention. All of the features and the combinations thereof described in the embodiment are not necessarily essential to the invention. 
       FIRST EMBODIMENT 
       [0038]      FIG. 1  is a diagram showing a semiconductor device  100  according to an embodiment of the present invention, as viewed from the electrode-pad side. The semiconductor device  100  has a CSP structure. In the diagram, the semiconductor device  100  includes: a plurality of electrode pads  10  for inputting and outputting signals from/to exterior; solder bumps  20  for making external lead electrodes; and rewiring  30 . 
         [0039]      FIG. 2  is a sectional view taken along the line  2 - 2  of  FIG. 1 . This semiconductor device  100  has the WL-CSP structure in which external connection electrodes are formed directly on its semiconductor substrate  40 . The semiconductor device  100  includes the semiconductor substrate  40 , a protective film  42  for passivation, the electrode pads  10 , the rewiring  30 , posts  48 , the solder bumps  20 , and a sealing resin  50 . Semiconductor integrated circuits including such devices as a transistor are formed on the top of the semiconductor substrate  40 , and are provided with the electrode pads  10  intended for signal input and output. The electrode pads  10  are typically made of such a material as aluminum. 
         [0040]    The protective film  42  is a nitrided silicon film or the like, which is formed to have openings above the electrode pads  10 . The rewiring  30  is made of copper, aluminum, gold, or the like. The rewiring  30  routes signals from the electrode pads  10  to the positions of the solder bumps  20 , which are the final positions of formation of the external lead electrodes, and connects the same to the posts  48 . The columnar posts  48  are made of gold, copper, or the like, and establish electric connection between the solder bumps  20  and the rewiring  30 . Incidentally, an insulating layer made of an oxide film, polyimide, or the like may also be formed over the protective film  42 , in which case the rewiring  30  is formed thereon. 
         [0041]    Return now to  FIG. 1 . In  FIG. 1 , the solder bumps  20  are arranged in two rows along the periphery of the semiconductor substrate  40 . The electrode pads  10  are arranged inside the outermost solder bumps so as to be interposed between the two rows of solder bumps. 
         [0042]    Each of the traces of the rewiring  30  is extended from an electrode pad  10 , and is connected to any one of the outermost solder bumps  20  or the inner solder bumps  20 . 
         [0043]    According to the present embodiment, the outermost solder bumps and the inner solder bumps both can be connected with the electrode pads  10  by approximately the same distances of rewiring. In addition, since the rewiring  30  does not fall outside the outermost solder bumps, the outermost solder bumps can be located close to the edges of the semiconductor substrate  40  without constraints from the layout of the rewiring  30  as far as allowed by the rules of the manufacturing process. It is therefore possible to suppress an increase in chip size. 
       SECOND EMBODIMENT 
       [0044]    The semiconductor device  100  according to this second embodiment is characterized by that the solder bumps  20  and the rewiring  30  are arranged systematically.  FIGS. 3A to 3C  show part of the layout of the electrode pads  10 , the solder bumps  20 , and the rewiring  30  on the semiconductor device  100  according to the present embodiment. 
         [0045]    Each of the areas shown in  FIGS. 3A to 3C  represents one of four areas  300   a  to  300   d  having the same shapes, corresponding to the respective sides of a rectangular, shown by the broken lines in  FIG. 3D . In  FIGS. 3A to 3C , both the electrode pads  10  and the solder bumps  20  are arranged at regular intervals. 
         [0046]    In  FIGS. 3A and 3B , the solder bumps  20  are arranged linearly in two parallel rows at regular intervals. The electrode pads  10  are arranged linearly in the area interposed between the two rows of solder bumps. The electrode pads  10  are spaced at approximately ½ the spacing of the solder bumps  20 . 
         [0047]    With the traces of rewiring  30 , the respective electrode pads  10  are connected to outer and inner ones out of the two rows of solder bumps  20  alternately in generally the same distances. 
         [0048]    In  FIG. 3C , the electrode pads  10  are also arranged linearly in two parallel rows. Each of the electrode pads  10  is connected to a nearest solder bump  20  via a trace of rewiring  30 . 
         [0049]    According to the present embodiment, the traces of the rewiring  30  can be laid generally straight with a reduction in the wiring length. It is also possible to suppress variations in the wiring lengths to the respective terminals, i.e., in the resistances and inductances of the traces. Besides, the rewiring  30  can be laid in a systematic fashion, except those traces of the rewiring  30  to be connected with the solder bumps  20  at the ends of the linear arrangements. 
         [0050]    With the layouts shown in  FIGS. 3A and 3B , the electrode pads  10  can be arranged linearly in each single area, and thus into a rectangular configuration in terms of the entire semiconductor device  100 . It is therefore possible to enhance the consistency with conventional design patterns. 
         [0051]    Furthermore, with the layout shown in  FIG. 3C , the distances between the electrode pads  10  and the solder bumps  20  can be made generally identical at every location. This can further reduce variations in the wiring length as compared to the layouts shown in  FIGS. 3A and 3B . As a result, it is possible to suppress variations in the circuit characteristics of the semiconductor device  100  regardless of which signals are associated with which electrode pads  10 . 
         [0052]    In the present embodiment, each individual area shown by the broken lines in  FIG. 3D  may be sectioned in a different configuration such as two rows by five columns (or five rows by two columns). 
       THIRD EMBODIMENT 
       [0053]    The semiconductor device  100  according to a third embodiment provides a method of making effective use of the space above a semiconductor integrated circuit, appearing outside the electrode pads  10  in the first and second embodiments. 
         [0054]      FIGS. 4A and 4B  are plan views of part of the semiconductor device  100  according to the third embodiment, showing the layouts before and after packaging, respectively. As shown in  FIG. 4A , before packaging, a semiconductor integrated circuit including the electrode pads  10 , a functional circuit  60 , and input/output circuits  70  is formed on the top of the semiconductor substrate  40 . The electrode pads  10 , the functional circuit  60 , and the input/output circuits  70  are connected by ordinary wiring  80  inside the semiconductor integrated circuit. 
         [0055]    The functional circuit  60  is a functional block for performing signal processing in the semiconductor integrated circuit. The functional circuit  60  varies in configuration and in area depending on its design. 
         [0056]    On the other hand, the input/output circuits  70  are circuit blocks to be connected with the electrode pads  10  for inputting and outputting signals. The input/output circuits  70  include diodes, capacitors, and other protection circuits for protecting the internal circuit elements, and input/output buffer circuits. These protective elements and input/output buffers are composed of basic blocks which have transistors, diodes, capacitors, and other elements arranged in a predetermined configuration, with almost fixed sizes. 
         [0057]    As shown in  FIG. 4B , since the electrode pads  10  are arranged inside the outermost solder bumps  20 , space  420  appears in the peripheral area of the semiconductor substrate  40 . This space  420  is utilized to arrange the input/output circuits  70 . In the present embodiment, it is desirable to estimate the amount of space to appear outside the electrode pads  10  before designing each input/output circuit  70  into a shape to fit in this space. 
         [0058]    According to the present embodiment, the input/output circuits  70  are disposed to the space  420  above the semiconductor integrated circuit, appearing outside the electrode pads  10 . This makes it possible to reduce variations ascribable to the rewiring and decrease the chip size of the semiconductor device  100 . 
         [0059]    Moreover, when the semiconductor device  100  is redesigned to change the function or size of the functional circuit  60 , the layout of the electrode pads  10 , the solder bumps  20 , and the rewiring  30  can be used intact to shrink the design period. 
         [0060]    In digital circuits, it is often the case that the circuit block constituting each single unit, such as a gate array, has a fixed circuit configuration and a fixed size. Then, such circuit blocks may be disposed to the peripheral space  420  instead of the input/output circuits  70 . 
         [0061]    The foregoing embodiments have been given solely by way of example. It will be understood by those skilled in the art that various modifications may be made to combinations of the foregoing components and processes, and all such modifications are also intended to fall within the scope of the present invention. 
         [0062]    The embodiments have dealt with the cases where the solder bumps are arranged in two rows along the periphery of the semiconductor device  100 . This is not restrictive, however. For example, the solder bumps may be arranged in two rows along each of two opposite sides out of the four sides of the semiconductor device  100 . In this case, electrode pads can be arranged in the area interposed between the two rows on each side. The embodiments may be applied to one of the four sides alone. 
         [0063]    Moreover, even when solder bumps are arranged in any arbitrary configuration, such as a matrix of four rows by eight columns and a matrix of eight rows by eight columns, the effects of the present invention can be obtained by grouping the solder bumps in two rows and arranging electrode pads therebetween. 
         [0064]    Furthermore, the semiconductor device  100  may be configured so that external connection is established via the posts  48  alone, without the formation of the solder bumps  20 . An alloy layer may also be formed between the posts  48  and the solder bumps  20 , or between the posts  48  and the rewiring  30 , for the sake of preferable electric and physical connection properties. 
         [0065]    The embodiments are applicable to any of analog circuits, digital circuits, and analog-digital hybrid circuits. 
         [0066]    While the preferred embodiments of the present invention have been described using specific terms, such description is for illustrative purposes only, and it is to be understood that changes and variations may be made without departing from the spirit or scope of the appended claims.