Abstract:
In one embodiment there is provided a motherboard assembly. The motherboard assembly comprises a motherboard substrate; a conductive circuit on a first side of the motherboard substrate comprising an interface to connect the conductive circuit to an electrical component; and a power leveling element aligned with the interface and mounted to a second side of the motherboard substrate opposite the first side, the power leveling element being to level power delivery from the interface.

Description:
FIELD OF THE INVENTION  
         [0001]    This invention relates to motherboards. In particular, it relates to power routing in motherboards.  
         BACKGROUND  
         [0002]    As used herein, the term “motherboard” refers generally to any carrier for circuits or components. Generally, a motherboard comprises a motherboard substrate and a conductive circuit printed thereon to route power from a power supply to a electrical component, e.g., a microprocessor, mounted on the motherboard. The electrical component may be mounted on a surface of the motherboard, or it may be mounted within a socket in the motherboard. In the case of a surface mounting, electrical interconnection elements such as pins or gold-plated lands of the electrical component mate with complementary socket formations to electrically interconnect the electrical component to the motherboard. In the case of a surface mounting, a ball grid array (BGA) comprising a plurality of solder balls is soldered into electrical contact with the motherboard.  
           [0003]    The electrical interconnection elements may be disposed to define a power routing configuration, wherein some of the electrical interconnection elements occur at opposed ends of the electrical component. Thus, the electrical interconnection elements at one end of the electrical component may be closer to a power supply than the electrical interconnection elements at the opposite end of the electrical component. For example, in one power routing configuration, the electrical interconnection elements may be in the form of pins located at a north and south end of the electrical component. The pins at the north end will hereinafter be referred as to the “north pins”, and the pins at the south end will hereinafter be referred to as the “south pins”. Even in a power routing configuration in which all the electrical interconnection elements are located at one end of the electrical component, the electrical interconnection elements may have a spacial configuration such that some of the electrical interconnection elements may be located closer to the power supply than others.  
           [0004]    These power routing configurations result in a non-uniform current flow through the north and south pins, respectively. This is illustrated in FIG. 1 of the drawings, which shows a simplified circuit for current flow through a motherboard.  
           [0005]    Referring to FIG. 1, V represents the voltage supplied by the power supply, R MB  represents the motherboard resistance, R South  and R North  represent the resistance of the north and south pins, respectively.  
           [0006]    Assuming R South =R North =R, then the current flowing through the south pins and north pins, is expressed as Equation 1 and Equation 2 below, respectively.  
               I   South     =       I     l                 n       *     (     R       (     R   +     R   MB       )     +   R       )               [     Equation                 1     ]                 I   North     =       I     l                 n       *     (       R   +     R   MB           (     R   +     R   MB       )     +   R       )               [     Equation                 2     ]                               
 
           [0007]    The ratio of these currents, expressed in Equation 3, indicates the level of non-uniformity in current flowing through the north and south pins.  
             Ratio   =         I   South       I   North       =     R     R   +     R   MB                   [     Equation                 3     ]                               
 
           [0008]    When the motherboard resistance is extremely low, i.e. R MB →0; Ratio=1 then the current flowing through each side is uniform. When the motherboard resistance is extremely high, i.e., when R MB →∞; Ratio=0 then all the current flows through the south side and therefore is extremely non-uniform.  
           [0009]    The conductive circuit provides a conductive path between a respective pair of north and south pins. The resistance of each of these paths, determines the magnitude of the current flow therethrough, as discussed above. Thus, non-uniformity in these resistances cause corresponding non-uniformity of current flow through each of the parts, as discussed above. The consequence of this non-uniform current flow is that it leads to non-uniform power dissipation, and heating, which raises potential reliability problems.  
           [0010]    This problem of the non-uniform current flow occurs whenever there is a power routing configuration in which some of the electrical interconnection elements are closer to a power supply than other electrical interconnection elements. Thus, this problem may occur in a power routing configuration that has north and south pins, as discussed above, east and west pins, solder balls disposed in a ball grid array, or in the case of conductive lands in a land grid array (LGA).  
           [0011]    One attempt to solve this problem of non-uniform current flow is to increase the number of layers within the motherboard, each layer carrying a conductive circuit. Another attempt at solving the problem of non-uniform current flow is to increase the density of current paths within a circuit on the motherboard. Each of these solutions are expensive to implement.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]    [0012]FIG. 1 shows a prior art technique of addressing the non-uniform distribution of current to an electrical element;  
         [0013]    [0013]FIG. 2 shows an exploded perspective view of a motherboard assembly in accordance with one embodiment of the invention; and  
         [0014]    [0014]FIG. 3 shows a side view of the motherboard assembly of FIG. 2.  
     
    
     DETAILED DESCRIPTION  
       [0015]    In the following description, for purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of the invention. It will be apparent, however, to one skilled in the art that the invention can be practiced without these specific details. In other instances, structures and devices are shown in block diagram form in order to avoid obscuring the invention.  
         [0016]    Reference in this specification to “one embodiment” or “an embodiment” means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the invention. The appearances of the phrase “in one embodiment” in various places in the specification are not necessarily all referring to the same embodiment, nor are separate or alternative embodiments mutually exclusive of other embodiments. Moreover, various features are described which may be exhibited by some embodiments and not by others. Similarly, various requirements are described which may be requirements for some embodiments but not other embodiments.  
         [0017]    [0017]FIG. 1 of the drawings shows a side view of a high level block diagram of a motherboard assembly  10  comprising an electrical component in the form of a microprocessor  12 , which is surface mounted via solder balls  14  to an upper surface  16  of a motherboard  18 . Each solder ball  14  is in electrical contact with a power routing circuit  22  of the motherboard  18  which routes power from a power supply  24  to each of the solder balls  14 . The solder balls  14  are disposed in an array comprising rows of solder balls such that a row of solder balls at one end of the microprocessor  12  is closer to the power supply  24  than a row of solder balls located at the opposite end of the microprocessor  12 . For example, the row of solder balls that is closer to the power supply  24  may be located at a north end of the microprocessor  12 , whereas the row of solder balls furthest from the power supply  24  may be located at a south end of the microprocessor  12 . In other configurations, the row of solder balls that is closest to the power supply  24  may be located at an east end of the microprocessor  12 , whereas the row of solder balls that is located furthest from the power supply  24  may be located at a west end of the microprocessor  12 . The exact designation of the solder balls as being located at an east, a west, a north or a south end of the microprocessor  12  is not important. What is important, however, is that the solder balls, which are representative of electrical interconnection elements and which may be electrical pins, electrical lands, etc., in other embodiments, are disposed in a spatial configuration, in which the solder balls at one end of the microprocessor  12  are closer to the power supply  24  than the solder balls at the opposite end of the microprocessor  12 .  
         [0018]    As a result of such a spatial configuration of the electrical interconnection elements, and as described above, there would be a non-uniform current distribution to the solder balls  14  such that the solder balls that are closest to the power supply  24  will have a higher current flow therethrough than the solder balls that are furthest away from the power supply  24 .  
         [0019]    As explained above, this non-uniform current flow leads to non-uniform power dissipation, and heating, which gives rise to reliability problems.  
         [0020]    According to techniques of the prior art, one technique which attempts to solve this problem includes adding layers, represented by reference numeral  26  in FIG. 1 of the drawings, to the motherboard  18 , wherein each layer comprises conductive circuitry which adds additional conductive pathways between the power supply  24  and the solder balls  14 . This solution is difficult to implement, and adds to the complexity of the motherboard  18 .  
         [0021]    Referring now to FIGS. 2 and 3 of the drawings, reference numeral  30  generally indicates a motherboard assembly in accordance with one embodiment of the present invention. The motherboard assembly  30  includes a motherboard  32  comprising an operatively upper surface  34 , and an operatively lower surface  36 . The motherboard assembly  30  further comprises an electrical component  38  which, could, for example, be a microprocessor. Electrical component  38  may be surface mounted to the upper surface  34  of the motherboard  32  through interconnection elements in the form of solder balls  39  disposed in a ball grid array (BGA). Alternatively, the electrical component  38  may be surface mounted within a socket which opens on the upper surface  34  of the motherboard  32 . The socket may be a land grid array (LGA) type socket and the electrical interconnection elements may be in the form of gold plated electrical lands. Alternatively, the electrical interconnection elements may be in the form of electrical pins which mate with complementary formations in a corresponding socket of the motherboard  32 .  
         [0022]    A power supply  40  routes power through a conductive circuit  42  to electrical interconnection elements.  
         [0023]    As noted above, whenever the electrical interconnection elements are disposed in a spatial configuration in which some of the electrical interconnection elements are closer to the power supply  40  than others, the problem of non-uniform current distribution occurs. In order to address this problem, the motherboard assembly  30  further comprises a conductive element  44  which is mounted to the underside  36  of the motherboard  32 , immediately under the electrical component  38 . The purpose of the conductive element  44  is to provide an alternative, non-motherboard electrical path through which current may be routed to the electrical interconnection elements that are furthest from the power supply  40 . In one embodiment, the conductive element  44  may be a planar conductive element and may include a conductive metal substrate, such as a copper substrate. In other embodiments, the conductive element may be in the form of a circuit board comprising conductive lines printed thereon. Electrical interconnection between the conductive element  44  and the underside  36  of the motherboard  32  may be achieved in various ways. For example, the conductive element  44 , which may be conveniently referred to as a power-leveler, may be connected to the underside  36  of the motherboard  32  through a surface mount process. The surface mount process may be accomplished by incorporation of solder balls on a surface of the power-leveler  44 . In the embodiment of the power-leveler shown in FIG. 2 of the drawings, reference numeral  46  indicates one embodiment of these solder balls. The solder balls may be attached to the motherboard  32  through the use of a standard paste print and reflow surface mount process.  
         [0024]    In another embodiment, the power-leveler (conductive element)  44  may take the form of a lead frame package comprising metal leads that are integrated within the package. This package may be surface mounted to the motherboard  32  through a standard paste print and reflow mount process.  
         [0025]    In yet a further embodiment, a Land Grid Array (LGA) socket type connection may be used to achieve electrical interconnection between the electrical (conductive element)  44  and the motherboard  32 . In this embodiment, the electrical interconnection lands may be located on the motherboard  32 , and the power-leveler (conductive element)  44  may comprise electrical contacts to provide an electrical connection when a sustained compressive load is provided between the motherboard and the power-leveler (conductive element)  44 .  
         [0026]    In yet another embodiment, the power-leveler (conductive element)  44  may be press-fitted into a complementary socket on the underside  36  of the motherboard  32 . For example, the motherboard  32  may be provided with holes, typically through-hole vias, and the power-leveler (conductive element)  44  may comprise metal leads so that the power-leveler (conductive element)  44  may be press fitted into the holes in the motherboard  32 .  
         [0027]    The exact method by which electrical interconnection between the electrical conductive element  54  and the underside  36  of the motherboard  32  may thus vary in different embodiments. However, in each case, when the electrical interconnection between the electrical conductive element  44  and the underside  36  of the motherboard  32  is achieved, there is provided an alternative non-motherboard pathway for the power to be routed to the electrical interconnection elements that are furthest from the power supply  40 .  
         [0028]    Although the present invention has been described with reference to specific exemplary embodiments, it will be evident that the various modification and changes can be made to these embodiments without departing from the broader spirit of the invention as set forth in the claims. Accordingly, the specification and drawings are to be regarded in an illustrative sense rather than in a restrictive sense.