Abstract:
An integrated voltage regulator may be provided on the bottom of a ball grid array processor package. This may be done despite the fact that conventionally integrated voltage regulator chips are too thick to fit in the area normally available between the motherboard and the ball grid array package because that area is defined by solder balls of a necessarily limited height which is conventionally believed to be too small to accommodate the integrated voltage regulator.

Description:
BACKGROUND 
       [0001]    This relates to computer systems and, more particularly, to providing supply voltages to power integrated circuits such as a processor. 
         [0002]    Advances in integrated circuit technology continue to provide faster, more robust, more densely packed integrated circuits. With each technological advance, power delivery, input/output, and thermal solutions become problematic. 
         [0003]    A socket may be used to couple a processor to a system board, such as a motherboard. A number of leads connect the various input/output ports on the processor to various buses, control lines, and power lines on the system board. Each lead has associated with it a certain amount of inductance. Inductance, related to the length of leads, must be below a certain critical inductance level in order for input and output operations to work properly. The critical inductance decreases as the operating frequency of the processor increases. The maximum allowable length of the leads tends to decrease as operating frequency increases. 
         [0004]    A voltage regulator provides the power delivery solution for the processor. Processors usually operate at different voltage levels and tolerance levels than those typically provided by most power supplies used in computer systems. 
         [0005]    Processors also commonly consume power at a higher rate than most power supplies provide. The amount of power that a processor consumes depends on clock speed and transistor density. A voltage regulator may not only convert power to appropriate voltage and tolerance levels, but also supplies power at the required slew rate. Capacitors may store power from the power supply so that it can be provided at a rate faster slew rate. The amount of capacitance needed to sustain the slew rate increases as the slew rate increases and increases as the distance between capacitors and the processor increases. Larger capacitance may mean larger and/or more capacitors must be provided. 
         [0006]    Because the voltage regulator needs to be as close as possible to the processor to provide power at the required slew rate and in an efficient manner, it is advantageous to use an integrated voltage regulator that provides power proximate to the processor. For example, in connection with pin grid array circuits, an integrated voltage regulator may be provided within a socket that couples the processor package to a motherboard. The socket provides sufficient vertical height to receive the integrated voltage regulator so that the voltage regulator can be mounted on the bottom of the pin grid array package. 
         [0007]    Increasingly, ball grid array packages are becoming more popular. They have many advantages, including lower costs and much smaller package sizes. However, ball grid arrays generally must have solder balls of a certain size to achieve the desired input/output density. As a result, the size of the solder balls tends to be too small to receive an integrated voltage regulator below the processor package. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]      FIG. 1  is an enlarged, partial, cross-sectional view of one embodiment of the present invention; 
           [0009]      FIG. 2  is an enlarged, partial, cross-sectional view of another embodiment of the present invention; and 
           [0010]      FIG. 3  is a system depiction for both embodiments of the present invention illustrated in  FIGS. 1 and 2 . 
       
    
    
     DETAILED DESCRIPTION 
       [0011]    Referring to  FIG. 1 , a computer system  10  may be formed on a system or motherboard  32 . A motherboard is a printed circuit board on which are mounted a number of components, including a processor. All or part of a computer system may be mounted on or below the motherboard. In particular, a processor package may be mounted with a ball grid array, flip chip, or C4 packaging on top of the motherboard  32 . The processor ball grid array package may be coupled by solder balls  22  to appropriate lands on the motherboard  32 . In addition, the solder balls  22  may electrically and mechanically couple to lands (not shown) on the ball grid array package  18 . The ball grid array package  18 , in turn, electrically couples to a processor integrated circuit  12  by solder balls  14 . Underfill material  16  may be provided between the processor integrated circuit  12  and the ball grid array package  18 , in one embodiment, to seal out atmospheric moisture. 
         [0012]    Some of the balls  14  on the integrated circuit  12  may connect via vias  20  through the package  18  to balls  26  on an integrated voltage regulator  28 . The integrated voltage regulator  28  may be a bare (unpackaged) die mounted on the bottom of the ball grid array package  18  so that it is in close proximity to the integrated circuit  12 . The integrated voltage regulator  28 , in some embodiments, may include not only the voltage regulator, but also on-chip decoupling capacitors, a pulse width modulation circuit, and the inductors integrated within one package. An underfill  24  may be provided between the voltage regulator  28  and the ball grid array package  18  to seal the region therebetween. 
         [0013]    The balls  22  must be of a certain size in order to obtain the desired density of inputs and outputs between the motherboard  32  and the integrated circuit  12 . As a result, in some cases, the solder ball height, for the desired input/output density, may be too small to fit the integrated voltage regulator  28  on the bottom of the package  18  without interfering with the motherboard  32 . Again, it is desirable to locate the integrated voltage regulator  28  on the bottom of the package  18  for the electrical performance reasons described previously. 
         [0014]    In one embodiment, a recess  30  may be formed in the motherboard  32  to receive the integrated voltage regulator  28  when the package is placed on the motherboard. For example, the package may be surface mounted to the motherboard. It may be positioned by a pick-and-place machine in the appropriate position on the motherboard. In this position, the integrated voltage regulator  28  fits in the recess  30 . Then heat may be applied to solder the package to the motherboard  32 , thereby fixing the integrated voltage regulator  28  at least partially within the hole  30  in the motherboard  32 . 
         [0015]    The motherboard recess  30  may be formed by various techniques, including drilling, etching, laser drilling, and punching. The recess  30  may partially or completely penetrate the motherboard  32 . 
         [0016]    In accordance with another embodiment, in a system  40 , also involving a ball grid array integrated circuit package and its securement to a motherboard with an intervening integrated voltage regulator, referring to  FIG. 2 , the integrated voltage regulator  34  may be made of a sufficiently reduced vertical height that it can actually fit within the region defined between the package  18  and the motherboard  32  by the height of the solder balls  22 . This may be achieved by reducing the thickness of the integrated voltage regulator die. This height reduction may be done by forming the die in conventional fashion and then simply grinding off the back side of the die to thin the die down to the thickness needed to fit within the gap between the ball grid array package and the motherboard  32 , given the necessary vertical height of the solder balls  22  once surface mounted to the motherboard and the ball grid array package. That is, generally the vertical height of the solder balls  22  will reduce as a result of surface mounting and it is this height that is critical in determining the final thickness of the integrated voltage regulator  34  die. 
         [0017]    As shown in  FIG. 2 , the integrated voltage regulator  34  may be thermally coupled to the motherboard  32  by a thermal interface material, such as a metal or ceramic based material, that may include a thermal pad and conducting grease  36  in one embodiment. Thus, a good thermal connection may be made from the integrated voltage regulator  34  to the motherboard  32 . The thermal pad may be graphite or self-gluing thermal tape, to mention two examples, while the conducting grease may, for example, include silicone. 
         [0018]    Formed through the motherboard  32  are a plurality of thermal vias  38 . The thermal vias  38  may be formed by drilling vias through the motherboard  38  and then filling the vias with a thermally conductive material, such as a metal, including one or more of copper, gold, or aluminum. As a result, heat is transmitted from the integrated voltage regulator  34  externally of the package and the motherboard. This heat may arise from the operation of the integrated voltage regulator  34 , as well as heat transferred from the integrated circuit  12  and otherwise blocked from dissipation by the intervening voltage regulator  34 . 
         [0019]    In both embodiments described above, conventionally, a heat sink would be provided over the integrated circuit  12  to dissipate heat upwardly away from the package. 
         [0020]    Referring to  FIG. 3 , a computer system may be formed in accordance with one embodiment. The computer system may include a processor  100  coupled to hub  110 . The processor  100  may be powered by one or more voltages from the voltage regulator  150 . The processor  100  may communicate with a graphics controller  105 , main memory  115 , and hub  125  via hub  110 . Hub  125  may couple peripheral device  120 , storage device  130 , audio device  135 , video device  145 , and bridge  140  to a hub  110 . The bridge  140  may couple hub  125  to one or more additional buses coupled to one or more additional peripheral devices. Note that in accordance with other embodiments of the present invention, the computer system may include more or fewer components than those shown in  FIG. 3  and may include a vast variety of other components arranged in any of a variety of architectures. 
         [0021]    In accordance with one embodiment, the voltage regulator  150  is an integrated voltage regulator that is external to the processor  100 . The voltage regulator  150  may provide one or more supply voltages to the processor  100  alone or in addition to providing one or more supply voltages to other components of the computer system. In addition, there may be one or more additional voltage regulators that provide one or more additional supply voltages to the processor. The voltage regulator may be an integrated voltage regulator, as in the case of the voltage regulators  28  and  34 , shown in  FIGS. 1 and 2 . The processor may be implemented by the ball grid array package  18  and the integrated circuit  12  in some embodiments of the present invention. 
         [0022]    Thus, in some embodiments, the voltage regulator may be thicker in a vertical direction than the solder balls joining the package to the board. In one such embodiment, the system board may include a recess to accommodate the regulator. In some embodiments, the recess may extend completely through the system board. In other cases, the recess may not extend all the way through the board. If the recess does not extend completely through the board, a thermal via may be installed under the voltage regulator through the remaining portion of the board, below the recess. 
         [0023]    In some embodiments, the regulator may have a thickness in the vertical direction that is less than or equal to the vertical height of the solder balls when coupled between the board and the package. In such cases, a thermal interface material may be used between the board and the regulator. In some cases, the thermal interface may be used to conduct heat through the board from said voltage regulator. 
         [0024]    As still another possibility, a donut-shaped interposer may be used to extend the solder balls and to pass the regulator through a central opening in the interposer. The interposer may be positioned between the package  18  and the board  32 . It may be coupled by solder balls to the board and the package. The interposer may provide additional vertical space to accommodate the voltage regulator. 
         [0025]    References throughout this specification to “one embodiment” or “an embodiment” mean that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one implementation encompassed within the present invention. Thus, appearances of the phrase “one embodiment” or “in an embodiment” are not necessarily referring to the same embodiment. Furthermore, the particular features, structures, or characteristics may be instituted in other suitable forms other than the particular embodiment illustrated and all such forms may be encompassed within the claims of the present application. 
         [0026]    While the present invention has been described with respect to a limited number of embodiments, those skilled in the art will appreciate numerous modifications and variations therefrom. It is intended that the appended claims cover all such modifications and variations as fall within the true spirit and scope of this present invention.