Abstract:
In one embodiment, the present invention includes a method of mounting a semiconductor device to a first side of a circuit board; and mounting at least one voltage regulator device to a second side of the circuit board, the second side opposite to the first side. The voltage regulator devices may be output filters, inductors, capacitors, and the like. In certain embodiments, the devices may be located directly underneath the semiconductor device.

Description:
BACKGROUND 
   The present invention relates to voltage regulators (VRs), and more specifically to placement of VR components in a system. 
   Voltage regulators are used in systems such as a personal computer (PC) (e.g., a desktop computer, server computer, notebook computer and the like) to receive input direct current (DC) voltages of a given voltage and convert and regulate such DC voltages to one or more regulated voltage levels required by various system components, such as integrated circuits (ICs) and the like. 
   In a typical system, for example, a desktop PC, a motherboard is used to support various system components, including ICs, connectors, VR components, and the like. Such VR components may include output inductors, bulk capacitors, metal oxide silicon field effect transistors (MOSFETs), driver ICs, and the like. Typically, the VR components are placed on a primary side (e.g., a topside) of the motherboard. These VR components must be placed outside an IC device&#39;s keepout zone (i.e., the IC&#39;s footprint, including any socket or heatsink retention). This placement can result in larger loadline lengths and therefore higher loadline impedance (i.e., capacitance, inductance, and resistance). In such manner, VR components may be located many centimeters away from an intended load (e.g., an IC). Accordingly, motherboard/package lateral travel dominates, increasing loadline length and therefore impedance. 
   Instead of the above described placement of VR components, other systems use some type of additional VR daughter module (i.e., a separate circuit board) that is plugged into the motherboard or an IC device. However, such additional circuit boards increase cost and complexity, and further increase the size of a given form factor. Furthermore, such designs typically provide inferior performance. A need thus exists to provide VR components that have reduced loadline length and impedance. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a cross-sectional view of a circuit board of a system in accordance with one embodiment of the present invention. 
       FIG. 2  is a plan view of a layout of a circuit board having an integrated circuit and voltage regulator components in accordance with one embodiment of the present invention. 
       FIG. 3  is a close-up view of a portion of the circuit board of  FIG. 2 . 
   

   DETAILED DESCRIPTION 
   In various embodiments of the present invention, different components of a voltage regulator may be coupled to a secondary side of a circuit board, such as a motherboard. More specifically, such components may be placed within a keepout zone of an IC located on the primary side of the circuit board. For example, a processor of a system may be coupled to a motherboard by a socket. Such a socket may have a keepout zone associated therewith on the primary side that prevents any other component from being located within the keepout zone. Thus, by locating one or more voltage regulator components on a secondary side of the circuit board, such components may be located closer to their load (i.e., the microprocessor) than if the components were located on the primary side of the circuit board. In such manner, a substantially shorter loadline and therefore a smaller loadline impedance may be accommodated. 
   While the types of components that may be placed on the secondary side may vary, in certain embodiments such components may include output inductors, board bulk and high-frequency (HF) capacitors, and one or more MOSFETs. Such location of voltage regulator components may improve current and voltage transients, provide for better power delivery efficiency, and lower operating temperatures for a voltage regulator. Furthermore, such location may also enable operation at higher current levels. Further, by providing such components on a secondary side of a circuit board, additional space may be open on the primary side, which either frees up space or permits use of a smaller circuit board to support all desired components. 
   Referring now to  FIG. 1 , shown is a cross-sectional view of a circuit board of a system in accordance with one embodiment of the present invention. As shown in  FIG. 1 , circuit board  20  may support multiple components. As shown in  FIG. 1 , some components may be surface mounted onto the circuit board, while others may be mounted by use of conductive through-holes within the circuit board. Circuit board  20  may be any desired circuit board, such as a motherboard of a PC. For example, circuit board  20  may be a four-layer motherboard for a desktop computer, although the scope of the present invention is not so limited. 
   As shown in  FIG. 1 , a primary side (i.e., the upper side) of circuit board  20  supports a semiconductor device  30  (also referred to herein as “IC  30 ”), which may be coupled to circuit board  20  via a package  35 . Package  35  may provide connections to pins of semiconductor device  30 . In one embodiment, semiconductor device  30  may be a microprocessor, such as a central processing unit (CPU) of the system. In turn, package  35  may be coupled to a socket  38  that may be formed of a housing that includes conductors to couple connections from semiconductor device  30  to connections on circuit board  20 . 
   An integrated heat spreader  37  may be mounted to package  35  (e.g., via an epoxy) and coupled to semiconductor device  30  to aid in cooling. In turn, a heat sink (not shown in  FIG. 1 ) may be coupled to integrated heat spreader  37  to provide heat dissipation. Such a heat sink may provide retentions to circuit board  20 . As shown in  FIG. 1 , package  35  may form a keepout zone. That is, the dimensions of package  35  define an area within which components typically cannot be mounted on circuit board  20 . 
   To reduce loadline impedance and provide better voltage regulator operation, multiple voltage regulation components may be coupled to a secondary side (i.e., the lower side) of circuit board  20 . As shown in  FIG. 1 , such components may include a plurality of bulk capacitors  41  and a plurality of output inductors  46 . Collectively, capacitors  41  and inductors  46  may form one or more output inductor-capacitor (LC) filters used as output filters for a voltage regulator. Such a voltage regulator may be a single regulator with multiple phases. In other embodiments, multiple regulators may be present, each having multiple phases. In certain embodiments, such an LC filter may be located directly under semiconductor device  30  and may provide a relatively short low impedance path to the load. In some embodiments such an impedance path may be only a few millimeters, for example, between two and five millimeters. 
   Further shown in  FIG. 1 , the secondary side of circuit board  20  may support multiple MOSFETs  51   b . In certain embodiments, MOSFETs  51   b  may act as synchronous FETs (SYNC FETs) that may be used in setting up and controlling a pulse width modulation (PWM) of the voltage regulator. While these secondary side components are shown for purposes of illustration in  FIG. 1 , it is to be understood that in other embodiments more, fewer or different components may be located on a secondary side of a circuit board and substantially within or near a keepout zone of an IC on the primary side. 
   Still referring to  FIG. 1 , additional components may be located on the primary side of circuit board  20 . Such components may include a plurality of HF capacitors  44  that may act as decoupling capacitors. Further, a plurality of MOSFETs  51   a  may be located at an immediate periphery of package  35 . Such MOSFETs  51   a  may be control FETs (CTRL FETs) used in controlling the PWM of the voltage regulator. Further components may include bulk capacitors  55   a  and  55   b  that may be used to filter incoming unregulated voltages to circuit board  20 . 
   In other embodiments, SYNC FETs  51   b  maybe on the primary side of a circuit board and CTRL FETs  51   a  may be on the secondary side. In still other embodiments, both types of FETs may be present on a secondary side of a circuit board. 
   Further shown in  FIG. 1  is a connector  60  that is coupled to receive one or more source voltages, for example, from a power supply of the system. Such voltages may then be converted to voltages used by components on circuit board  20 . For example, a 12 volt level may be converted to a lower voltage, such as a 1.3 or 0.9 volt level used by a microprocessor. 
   Referring now to  FIG. 2 , shown is a plan view of a layout of a circuit board having an integrated circuit and voltage regulator components in accordance with one embodiment of the present invention. In the embodiment of  FIG. 2 , the VR components may be associated with a multiple phase voltage regulator, and more specifically a six-phase regulator, although the scope of the present invention is not so limited. 
   As shown in  FIG. 2 , IC  30  may be mounted to package  35 , which in turn maybe mounted via a socket (not shown in  FIG. 2 ) and a retention mechanism  36  to a top side of a circuit board  20 . Interconnects of IC  30  may form a pin field within the boundaries of IC  30 . IC  30  may have packaging in accordance with a land grid array (LGA) type package, although the scope of the present invention is not so limited. For example, in other embodiments, a ball grid array (BGA) package or a pin grid array (PGA) package may be used. The term “pin” is used herein to refer to any type of interconnect, and it is to be understood that such interconnects may be pins, balls, pads or other types of interconnects, in different embodiments. 
   Still referring to  FIG. 2 , IC  30  may be supported and coupled to a package  35  that in turn is coupled via board retention  36  to circuit board  20 . While not shown in  FIG. 2 , it is to be understood that an integrated heat spreader may support heat sink and other thermomechanical components. 
   As shown in  FIG. 2 , various voltage regulator components may be positioned on a secondary side of motherboard  20 , and certain of these components may be located within the keepout zone of package  35 . For example, a plurality of synchronous MOSFETs  51   b  may be located on the secondary side. Furthermore, a plurality of output inductors may be located on the secondary side at a substantial periphery of pin field  33 . Note for ease of illustration only pads  46  of a single inductor is shown in  FIG. 2 . Furthermore, bulk capacitors  41  may be coupled to the secondary side. As shown, bulk capacitors  41  may be located directly underneath IC  30  but outside of its pin field, in the embodiment of  FIG. 2 . Such bulk capacitor placement in general may improve VR stability. 
   Additional voltage regulator components that may be located on the secondary side may include a plurality of HF decoupling capacitors, one of which is shown in  FIG. 2  as HF capacitor  43 . As will be discussed below, such capacitors may be positioned between multiple planes of circuit board  20 . Additional HF capacitors  44  may be coupled to a primary side of circuit board  20 . Specifically, as shown in  FIG. 2 , primary side HF capacitors  44  may be located directly under the pin field (and substantially in the middle thereof), and in an unpopulated portion of the pin field. 
   Other voltage regulator components may be coupled to the primary side of circuit board  20 . Such components may include a plurality of CTRL MOSFETs  51   a , which may be coupled just outside a keepout zone of package  35 . As shown, such CTRL MOSFETs  51   a  may be located substantially adjacent to SYNC MOSFETs  51   b  (although on the other side of circuit board  20 ). 
   Further shown in  FIG. 2  are shaded regions corresponding to different planes of circuit board  20 . Such planes may be various layers of circuit board  20  and corresponding interconnects of the pin field. While referred to herein as “planes” of circuit board  20 , it is to be understood that such planes have corresponding areas in the pin field. As shown in  FIG. 2 , such planes may include a PWM plane  21  that may be used to couple CTRL MOSFETs  51   a  to corresponding SYNC MOSFETs  51   b , a ground plane  22  and a Vcc plane  23  (i.e., a supply voltage plane). As shown in  FIG. 2 , PWM plane  21  may have an area that extends from a periphery of ground area  22  to couple SYNC MOSFETs  51   b  to CTRL MOSFETs  51   a.    
   As shown in  FIG. 2 , the pin field may be formed of highly consolidated power and ground areas with substantial crenellations therebetween. Ground plane  22  may be situated substantially around a periphery of the pin field of IC  30 . Ground plane  22  may have a plurality of crenellations formed therein that provide extensions to abut portions of PWM plane  21  on a peripheral side, and on a proximal side such crenellations may abut a similar crenellated pattern of Vcc plane  23 . In such manner, ground plane  22  acts as an intermediate area between Vcc plane  23  and PWM plane  21 , and ground plane  22  acts as a moat around Vcc plane  23 . 
   In one embodiment, output inductors may have dimensions of approximately 0.25 inches by 0.25 inches, although the scope of the present invention is not so limited. As shown in  FIG. 2  (and in a close-up in  FIG. 3 ), in such an embodiment a PWM side inductor pad  46  (in  FIG. 2 ) sits just outside pin field  33 , while a Vcc side inductor pad  46  (in  FIG. 2 ) sits within pin field  33 . The crenellations provide a connection to such inductors and also provide a better opportunity to place HF decoupling capacitors directly between the Vcc input and the ground return planes. 
   Still referring to  FIG. 2 , the overall VR loadline may be reduced by placing SYNC FETs  51   b  on the secondary side within the keepout zone of package  35 . Since the socket to SYNC FET conduction path should carry roughly as much current as the Vcc line, such placement may have a substantial impact on reducing the overall loadline. Due to space constraints, this embodiment may place CTRL FETs  51   a  on the primary side outside the socket keepout zone, although the scope of the present invention is not so limited. 
   Referring now to  FIG. 3 , shown is a plan view of circuit board  20  of  FIG. 2  and components attached thereto. More specifically,  FIG. 3  is a close-up of the embodiment of  FIG. 2 .  FIG. 3  shows in more detail a portion of the crenellation pattern between Vcc plane  23  and ground plane  22 . As shown in  FIG. 3 , the crenellations may be of a substantially identical depth and width. While shown in the embodiment of  FIG. 3  as being four socket pins deep and four (and five) socket pins wide, it is to be understood that the scope of the present invention is not so limited, and different crenellation patterns may be present in different embodiments. As shown in  FIG. 3 , the pin field may be formed of a plurality of primary side socket pins  36  (one of which is designated reference number  36  in  FIG. 3 ). 
   Also shown in  FIG. 3  are various voltage regulator components coupled to both the primary and secondary sides of circuit board  20 . The primary side components include HF capacitors  44  within Vcc plane  23 . Secondary side components include HF capacitors  43  which as shown, are located between Vcc plane  23  and ground plane  22 . Placement of the HF capacitors within the pin field may improve performance by lowering the capacitors&#39; parasitic loadline. Similarly, output inductors  47  (one of which is shown for illustration in  FIG. 3 ) may be located such that a PWM side inductor pad  46   a  is located just outside of the pin field, while the Vcc side inductor pad  46   b  sits within the pin field, and more specifically within Vcc area  23 . Note pads  46   a  and  b  are shown coupled to a top inductor in  FIG. 3 . 
   Thus by placing key VR components on the motherboard&#39;s secondary side, VR components may be located substantially underneath an IC device. As a result, the loadline length may be significantly shorter, resulting in a substantial drop in loadline impedance from the VR to the IC device. This reduction may result in better current and voltage transients, better power delivery efficiency and lower VR temperatures. It may also help enable higher current levels (e.g., approximately 150 amperes and more, in certain embodiments). 
   Also, in systems where form factor is important, VR component placement in accordance with an embodiment of the present invention may free up more motherboard space, due to the movement of key VR components to the secondary side and underneath the socket keep-out. 
   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.