Abstract:
Provided is a method and system for designing an integrated circuit (IC) substrate, the substrate being formed to include at least one die. The method includes providing at least portions of IC power and a grounding function on a metal 2 substrate layer and utilizing all of a metal 3 substrate layer for the grounding function. Portions of the metal 2 layer and a metal 4 layer are utilized for the IC power, wherein all of the IC power is centralized underneath the die.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application claims benefit to U.S. Provisional Application No. 60/752,592, filed on Dec. 22, 2005, entitled “Method and System for Innovative Substrate/Package Design for a High Performance Integrated Circuit Chipset” which is incorporated by reference herein in its entirety. 
     
    
     BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     The present invention relates generally to packaging of substrates for integrated circuits (ICs).  
         [0004]     2. Background Art  
         [0005]     Traditional high speed substrate packaging can include high speed differential pair circuits routed on a metal 1 (M1) layer, metal 2 (M2) layer ground (GND), and metal 3 (M3) layer power (PWR) type structure. A metal 4 (M4) layer, in traditional substrate packaging, includes only ball pads, or signal. More specifically, power and GND balls are typically placed in the areas around the high speed differential pairs. However, achieving higher speeds from these traditionally packaged ICs (e.g., 1 giga-hertz (GHz) or greater) is problematic.  
         [0006]     Using the traditional substrate packaging structure noted above, the standard M4 layers cannot support the performance of higher speed chip applications. This is due, in part, to too many differential routes on the same layer, poor distribution of analog and core power, a need to increase package size to accomplish all differential pairs, and cross coupling between power and signal lines within the same block/layer.  
         [0007]     What is needed, therefore, is a method and system to ameliorate the challenges of the traditional IC packaging. More particularly, what is needed is an IC packaging system and method for accommodating higher speed differential pair circuit applications.  
       BRIEF SUMMARY OF THE INVENTION  
       [0008]     Consistent with the principles of the present invention as embodied and broadly described herein, the present invention includes a method for designing an integrated circuit (IC) substrate, the substrate being formed to include at least one die. The method includes providing at least portions of IC power and a grounding function on a metal 2 substrate layer and utilizing all of a metal 3 substrate layer for the grounding function. Portions of the metal 2 layer and a metal 4 layer are utilized for the IC power, wherein all of the IC power is centralized underneath the die.  
         [0009]     The present invention offers advantages including high speed differential pairs routed on the M1 and M4 layers with only GND balls around the high-speed pairs. The M2 layer (GND) includes embedded VDDC, the M3 layer (GND) includes embedded analog power, and the M4 layer has ball pads as well as different analog and core power planes. Additionally, the analog and core power paths are allocated in the center of the substrate—creating a very direct path into and out of the package. The technique of the present invention facilitates higher signal speeds within the differential pair circuits by reducing, among other things, cross-talk between the signal lines and the device power. Additional advantages of the present invention include substrate space saving based upon routing of the differential pairs on M1 and M4, more direct allocation of analog and core power (with a  4  layer BT substrate), reduction in overall package size and cost, and minimization of coupling between differential pairs on the top layer (M1) and the bottom layer (M2).  
         [0010]     As an example of reduction in overall package size, consider a package originally including a 40×40 4 layer plastic ball grid array (PBGA)+heat sink (HS) or 35×35 6-8 layer Flip chip BGA. By utilizing the substrate design techniques of the present invention, this package size can be reduced to a 35×35 4 layer PBGA+HS. This reduction is equivalent to a savings of two package sizes, in addition to providing higher package performance. By utilizing the present invention, cost effective substrate packaging can be implemented for many high-end high speed devices used in applications such as cable television, switching, and computer network servers.  
         [0011]     Further features and advantages of the present invention as well as the structure and operation of various embodiments of the present invention, are described in detail below with reference to the accompanying drawings. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS/FIGURES  
       [0012]     The accompanying drawings, which are incorporated herein and constitute part of the specification, illustrate embodiments of the present invention and, together with the general description given above and the detailed description of the embodiments given below, serve to explain the principles of the invention. In the drawings:  
         [0013]      FIG. 1  is an illustration of a traditional integrated circuit (IC) substrate packaging technique;  
         [0014]      FIG. 2  is an illustration of an M1 layer of the conventional IC substrate shown in  FIG. 1 ;  
         [0015]      FIG. 3  is an illustration of an M2 layer of the conventional IC substrate shown in  FIG. 1 ;  
         [0016]      FIG. 4  is an illustration of an M3 layer of the conventional IC substrate shown in  FIG. 1 ;  
         [0017]      FIG. 5  is an illustration of an M4 layer of the conventional IC substrate shown in  FIG. 1 ;  
         [0018]      FIG. 6  is an illustration of an IC substrate packaging technique in accordance with an embodiment of the present invention;  
         [0019]      FIG. 7  is an illustration of the M1 layer of the IC substrate shown in  FIG. 6  in accordance with the present invention;  
         [0020]      FIG. 8  is an illustration of the M2 layer of the IC substrate shown in  FIG. 6  in accordance with the present invention;  
         [0021]      FIG. 9  is an illustration of the M3 layer of the IC substrate shown in  FIG. 6  in accordance with the present invention;  
         [0022]      FIG. 10  is an illustration of the M4 layer of the IC substrate shown in  FIG. 6  in accordance with the present invention; and  
         [0023]      FIG. 11  is a flow diagram of an exemplary method of practicing an embodiment of the present invention.  
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0024]     The following detailed description of the present invention refers to the accompanying drawings that illustrate exemplary embodiments consistent with this invention. Other embodiments are possible, and modifications may be made to the embodiments within the spirit and scope of the invention. Therefore, the following detailed description is not meant to limit the invention. Rather, the scope of the invention is defined by the appended claims.  
         [0025]     It would be apparent to one skilled in the art that the present invention, as described below, may be implemented in many different embodiments of hardware, software, firmware, and/or the entities illustrated in the drawings. Any actual software code with the specialized controlled hardware to implement the present invention is not limiting of the present invention. Thus, the operation and behavior of the present invention will be described with the understanding that modifications and variations of the embodiments are possible, given the level of detail presented herein.  
         [0026]      FIG. 1  is an illustration of an integrated circuit (IC) substrate  100  using a traditional substrate packaging technique. With an increasing number of input/outputs (I/Os) and higher data rate signal transfers in semiconductors, there is an increased requirement for larger package sizes, more I/O on package pin outs, multiple layers for plane isolation, and different power consumption capabilities. In order to fulfill the increased requirements, very high-end substrates (e.g., over 6 to 8 layers) and very expensive substrates have traditionally been used.  FIG. 1  is an example of one of these traditional approaches.  
         [0027]     The structure of  FIG. 1  includes a number of high speed differential circuits. In  FIG. 1 , all differential pair circuits  102  are routed on an M1 layer  104 , with power and GND balls next to the pairs. This structure employs standard signal, ground, and power, signal substrate layering techniques. In  FIG. 1 , an expanded view  105  is provided. In the expanded view  105 , connections  106  shown are the differential pair circuits. Vdd connections  108  and GND connections  110  are indicated as shown. This approach will not ensure sufficient isolation for all of the differential pair circuits  102 . That is, placing power and ground around the differential pair circuits leaves an insufficient amount of space on the IC to combine and centralize power potentials. Furthermore, the traditional approach, using power and ground together, as illustrated in  FIG. 1 , does not provide adequate space to route an adequate number of high speed signal lines.  
         [0028]      FIG. 2  is a cross-sectional view  200  of the M1 layer  104  within the conventional IC substrate  100  shown in  FIG. 1 . The cross-sectional view  200  of  FIG. 2  indicates that the M1 layer  104  of traditional substrate includes signal, ground, and power components.  
         [0029]      FIG. 3  is an illustration of an M2 layer  300  of the conventional IC substrate  100  shown in  FIG. 1 . A cross-sectional view  302  in  FIG. 3  indicates that the M2 layer of traditional substrates is used exclusively for grounding.  
         [0030]      FIG. 4  is an illustration of an M3 layer  400  within the conventional IC substrate  100  shown in  FIG. 1 . A cross-sectional view  402  in  FIG. 4  indicates that the M3 layer of traditional substrates is used exclusively for power.  
         [0031]      FIG. 5  is an illustration of an M4 layer  500  of the conventional IC substrate  100  shown in  FIG. 1 . A cross-sectional view  502  in  FIG. 5  indicates that the M4 layer of traditional substrates is all signal. More particularly, the M4 layer  500  basically ball pads (i.e., no plane and no routing). That is, the M4 layer  500  has essentially no power and no ground. Also in  FIG. 5 , there are no signal lines on the bottom portion  504 , shown in the plane view on the left. Only ball pads are visible in the plane view.  
         [0032]      FIG. 6  is an illustration of an IC substrate  600  that embodies a packaging technique  602  in accordance with an embodiment of the present invention. In the present invention, a more cost effective packaging technique is used. In the present invention, instead of using the traditional M1-M4 structure of signal, ground, power, signal, the present invention centralizes the supply power and core power underneath the die.  
         [0033]     For example, in the present invention, all of the high speed differential pair circuits are located on M1 and M4 layers (illustrated more clearly below) as opposed to the power and ground structure of the conventional techniques, such as those illustrated in  FIGS. 1-5 . In the present invention, power and ground are kept away from the differential pairs, thus minimizing cross-talk. The approach of the present invention saves cost by eliminating the requirement of large packaging. This approach also provides significant space savings.  
         [0034]     More specifically, by running differential pair circuits on M1 and M4, more substrate real estate is freed up to run corresponding differential signals. In the present invention, an M2 layer is a combination of the Vdd core on the center, and ground. In the conventional substrate, such as the substrate  100  illustrated in  FIG. 2 , the M3 layer is used for power. The present invention, however, uses a mixed layer having power and ground on same layers, such as M1 and M2. In the present invention, high speed transmit differential pair circuits are placed on the M1 layer. Receive high speed (e.g. over 1 GHz) differential pair circuits are placed on the M4 layer.  
         [0035]     In  FIG. 6 , power is centralized beneath the die (i.e., on the area of the substrate that supports the die). In this manner, power need not be used on the substrate  600  in areas where grounds are also used.  
         [0036]     Placing all of the differential pairs on the M1 layer, as done in conventional structures, creates congestion that leads to cross-talk. In the present invention, however, by putting transmit differential pairs on the top and receive differential pairs on the bottom, cross talk can be reduced. In  FIG. 6 , only ground is next to the differential pairs. Additionally, the present invention uses a signal, ground, ground, signal structure. This structure facilitates faster speeds because of less coupling between power and signal lines.  
         [0037]      FIG. 7  is a more detailed illustration of an M1 layer  700  within the IC substrate  600  shown in  FIG. 6  in accordance with the present invention. A cross sectional view  702  of  FIG. 7  indicates that the M1 layer  700  includes a combination of signal, some power (i.e., because power is centralized), and ground. In order to centralize all of the supply power (i.e., beneath the die), a portion of the ground plane must be utilized.  
         [0038]      FIG. 8  is an illustration of an M2 layer  800  within the IC substrate  600  shown in  FIG. 6  in accordance with the present invention. A cross-sectional view  802  of  FIG. 8  indicates that the M2 layer  800  is part power and part ground. The M2 layer  800  is also power in order to facilitate the centralized power concept. In the conventional substrate structure (see for example,  FIG. 2 ), the M2 layer is all ground.  
         [0039]      FIG. 9  is an illustration of an M3 layer  900  within the IC substrate  600  shown in  FIG. 6  in accordance with the present invention. A cross sectional view  902  of  FIG. 9  indicates that all of the M3 layer  900 , in the present invention, is basically ground to ensure a proper return path on the ground plane. In the conventional approach, the M3 layer is power.  
         [0040]      FIG. 10  is an illustration of an M4 layer  1000  within the IC substrate  600  shown in  FIG. 6  in accordance with the present invention. A cross-sectional view  1002  of  FIG. 10  indicates that the M4 layer  1000  is a combination is signal and power. As noted above, the M4 layer includes receive differential pair circuits.  
         [0041]      FIG. 11  is an exemplary method  1100  of practicing an embodiment of the present invention. In  FIG. 11 , the method  1100  includes providing at least portions of IC power and a grounding function on a metal 2 substrate layer, as indicated in step  1102 . All of a metal 3 substrate layer is utilized for the grounding function, as indicated in step  1104 . In step  1106 , portion of the metal 2 layer and a metal 4 layer are utilized for providing IC power.  
       CONCLUSION  
       [0042]     The present invention has been described above with the aid of functional building blocks illustrating the performance of specified functions and relationships thereof. The boundaries of these functional building blocks have been arbitrarily defined herein for the convenience of the description. Alternate boundaries can be defined so long as the specified functions and relationships thereof are appropriately performed.  
         [0043]     Any such alternate boundaries are thus within the scope and spirit of the claimed invention. One skilled in the art will recognize that these functional building blocks can be implemented by analog and/or digital circuits, discrete components, application-specific integrated circuits, firmware, processor executing appropriate software, and the like, or any combination thereof. Thus, the breadth and scope of the present invention should not be limited by any of the above-described exemplary embodiments, but should be defined only in accordance with the following claims and their equivalents.  
         [0044]     The foregoing description of the specific embodiments will so fully reveal the general nature of the invention that others can, by applying knowledge within the skill of the art (including the contents of the references cited herein), readily modify and/or adapt for various applications such specific embodiments, without undue experimentation, without departing from the general concept of the present invention. Therefore, such adaptations and modifications are intended to be within the meaning and range of equivalents of the disclosed embodiments, based on the teaching and guidance presented herein. It is to be understood that the phraseology or terminology herein is for the purpose of description and not of limitation, such that the terminology or phraseology of the present specification is to be interpreted by the skilled artisan in light of the teachings and guidance presented herein, in combination with the knowledge of one of ordinary skill in the art.  
         [0045]     The Detailed Description section should primarily be used to interpret the claims. The Summary and Abstract sections may set forth one or more, but not all exemplary embodiments of the present invention as contemplated by the inventor(s), and thus, are not intended to limit the claims.