Patent Publication Number: US-2003224546-A1

Title: Method and apparatus for reducing noise in electrical power supplied to a semiconductor

Description:
BACKGROUND OF THE INVENTION  
       [0001] 1. Field of the Invention  
       [0002] This invention relates generally to reducing noise in an electrical power supply, and, more particularly, to a method and apparatus for providing localized filtering of electrical power.  
       [0003] 2. Description of the Related Art  
       [0004] Providing electrical power to electronic devices is becoming increasingly complex. Over time, voltage levels used to power various electronic devices have fallen dramatically. Many electronic components now operate at levels below 2 volts. As the operating voltage level has fallen, sensitivity to variations in the voltage level has become more significant. That is, variations that were once insignificant, as compared to the overall voltage level, now constitute a significant percentage variation in the supplied voltage.  
       [0005] These variations, or noise, may lead to faulty operation of the electronic component. That is, an electronic component operating at 5 Volts nominally may be capable of tolerating a 0.2 Volt variation without adversely affecting the operation of the electronic component. However, when the voltage level of the electronic component is at 2 Volts, the same 0.2 Volt variation is a 10 percent deviation, which may cause unpredictable and/or improper operation of the electronic component.  
       [0006] Historically, these variations have been removed, or at least reduced, by adding decoupling capacitors to filter or otherwise smooth the voltage provided to the electronic components. Typically, as shown in FIG. 1, decoupling capacitors  100  have been located adjacent an electronic component  102  to which electrical power is being supplied. Commonly, the capacitors  100  have been disposed on a printed circuit board  104  extending about the periphery of the component  102 , such as an integrated circuit device. All other things being equal, the closer the capacitors  100  are to the integrated circuit device  102 , the more substantial the effect they have on the electrical power delivered thereto. However, the number of capacitors  100  needed to prevent these relatively small variations in the supply voltage has become sufficiently large that it is problematic to locate enough capacitors sufficiently close to the device  102  in the region surrounding the device  102 .  
       SUMMARY OF THE INVENTION  
       [0007] In one aspect of the present invention, a method is provided for decoupling a voltage supply from a semiconductor device. The method comprises forming a pattern of spaced apart electrical connections on a first surface of a substrate wherein at least first and second ones of the connections are coupled to first and second terminals of the voltage supply respectively. A capacitor is located on a second surface of the substrate within the spaced apart connections, the capacitor having first and second leads coupled with the first and second ones of the connections. A semiconductor device is coupled to the substrate in mating relationship with the pattern of spaced apart electrical connections, wherein the capacitor is positioned adjacent the semiconductor device.  
       [0008] In another aspect of the present invention, an apparatus is provided. The apparatus is comprised of a substrate, a plurality of spaced apart electrical connections, a capacitor, and a semiconductor device. The plurality of spaced apart electrical connections are positioned on a first surface of the substrate wherein at least first and second ones of the connections are coupled to first and second terminals of a voltage supply respectively. The capacitor is coupled to a second surface of the substrate and positioned within the spaced apart connections. The capacitor has first and second leads coupled with the first and second ones of the connections. The semiconductor device is coupled to the substrate in mating relationship with the pattern of spaced apart electrical connections, wherein the capacitor is positioned adjacent the semiconductor device. 
     
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
     [0009] The invention may be understood by reference to the following description taken in conjunction with the accompanying drawings, in which the leftmost significant digit(s) in the reference numerals denote(s) the first figure in which the respective reference numerals appear, and in which:  
     [0010]FIG. 1 illustrates a perspective view of an electronic system that includes a plurality of capacitors arranged to reduce noise in a voltage supplied to a semiconductor device;  
     [0011]FIG. 2 schematically illustrates a cross sectional side view of a semiconductor device mounted on a printed circuit board;  
     [0012]FIG. 3 schematically illustrates an enlarged cross sectional side view of an embodiment of the semiconductor device and printed circuit board of FIG. 2;  
     [0013]FIG. 4 illustrates a top view of one embodiment the printed circuit board of FIGS. 2 and 3 in a region generally lying beneath the semiconductor device;  
     [0014]FIG. 5 illustrates a top view of an alternative embodiment the printed circuit board of FIGS. 2 and 3 in a region generally lying beneath the semiconductor device; and  
     [0015]FIG. 6 illustrates a cross sectional side view of the printed circuit board of FIGS.  2 - 5  in a region lying beneath the semiconductor device. 
    
    
     [0016] While the invention is susceptible to various modifications and alternative forms, specific embodiments thereof have been shown by way of example in the drawings and are herein described in detail. It should be understood, however, that the description herein of specific embodiments is not intended to limit the invention to the particular forms disclosed, but, on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the scope of the invention as defined by the appended claims.  
     DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS  
     [0017] Illustrative embodiments of the invention are described below. In the interest of clarity, not all features of an actual implementation are described in this specification. It will of course be appreciated that in the development of any such actual embodiment, numerous implementation-specific decisions must be made to achieve the developers&#39; specific goals, such as compliance with system-related and business-related constraints, which will vary from one implementation to another. Moreover, it will be appreciated that such a development effort might be complex and time-consuming, but would nevertheless be a routine undertaking for those of ordinary skill in the art having the benefit of this disclosure.  
     [0018] Illustrative embodiments of a method and apparatus for improving the supply of power to a semiconductor device are shown in FIGS.  2 - 6 . As will be readily apparent to those skilled in the art upon a complete reading of the present application, the present method and apparatus are applicable to a variety of electronic or electrical systems, including, but not limited to, logic devices, memory devices, processors, and the like.  
     [0019] Turning now to FIG. 2, a stylistic cross sectional side view of a conventional semiconductor device  200  mounted on a substrate, such as a printed circuit board  202  is shown. In the illustrated embodiment, an electrical connection  204  between the printed circuit board  202  and the semiconductor device  200  is a typical ball grid array. Those skilled in the art, however, will appreciate that other types of electrical connections may be employed without departing from the scope of the instant invention. For example, the electrical connection  204  may take the form of pins and sockets soldered or otherwise mechanically coupled together, or may include an intermediary device, such as a zero insertion force socket, or the like.  
     [0020] A physical mounting mechanism is not illustrated herein, as such devices are well known to those skilled in the art, and its inclusion in the drawing might serve to obfuscate the instant invention. Generally, it is sufficient to understand that the semiconductor device  204  is fixed to the printed circuit board  202  such that the electrical connection  204  is well established.  
     [0021] Generally, as shown in FIG. 3, the electrical connection  204  is comprised of a plurality of spaced-apart individual connectors  300  on the semiconductor device  200 , which are arranged in a pattern to mate with a corresponding plurality of spaced-apart individual connectors or pads  302  located on the printed circuit board  202 . The individual connectors  300 ,  302  provide electrical pathways between the semiconductor device  200  and the printed circuit board  202  such that information may be exchanged therebetween, and electrical power may be provided thereto. That is, at least one, and in some cases multiple ones, of the connectors  300  on the semiconductor device  200  are designed to receive a supply voltage (e.g., 2V, 5V, ground, etc.). That is, electrical power is supplied to the printed circuit board  202 , which, in turn, routes the electrical power through traces, wires, lines, etc. to the appropriate connector  302  on the printed circuit board  202 . The connector  302  passes the supply voltage to circuitry within the semiconductor device through the mating connector  300 .  
     [0022] One or more decoupling capacitors  304  are located on an opposite side of the printed circuit board  202  substantially below the semiconductor device  200 , as opposed to being positioned about the periphery of the semiconductor device  200 . In one embodiment, the decoupling capacitors  304  may extend interstitially relative to the array of connectors  302 . This interstitial spacing allows the decoupling capacitors  304  to be located in close proximity to the connectors  302  to which they are to be electrically coupled. In particular, the capacitors  304  may be located immediately adjacent the one or more connectors  302  that are coupled to receive the supply voltage. In the embodiment illustrated in FIG. 3, the capacitor  304  is shown positioned on a bottom surface of the printed circuit board  202 , opposite the semiconductor device  200 . The capacitor  304  is electrically coupled to connectors or pads  306  located on the bottom surface of the printed circuit board  202 . A via  308  extends through the printed circuit board  202 , establishing an electrical connection between the connectors  302 ,  306  located on opposite sides of the printed circuit board  202 . This embodiment allows the decoupling capacitors  304  to be located adjacent the connectors  302 .  
     [0023] Turning now to FIGS. 4 and 5, exemplary patterns of the connectors  302  and the decoupling capacitors  304  are illustrated. Generally, the capacitors  304  are positioned between the connectors  302  and adjacent those connectors  302  that are coupled to receive the supply voltage. For example, in the embodiment illustrated in FIG. 4, the capacitors  304  are positioned immediately about the connector  302   a , which is coupled in a conventional manner to a power plane (not shown) within the printed circuit board  202  to receive the supply voltage. Those skilled in the art will appreciate that more than one of the connectors  302  may be coupled to receive a supply voltage, and thus, one or more arrangements of decoupling capacitors  304  may be located adjacent each of these connectors  302  to ensure that noise, voltage droop, and other undesirable effects are reduced.  
     [0024] In the embodiment illustrated in FIGS. 4 and 5, the connectors  302  are configured in a conventional pattern that involves adjacent rows of the connectors  302  being misaligned or out of phase so as to provide a relatively dense but evenly distributed population of the connectors  302 . This configuration allows for multiple arrangements of the capacitors  304  within the spaces between the connectors  302 . For example, as shown in FIG. 4, each of the capacitors  304  may be located substantially within a single row of the connectors  302  in the space between adjacent ones of the connectors  302 . Likewise, although not illustrated, each of the capacitors  304  could be located substantially within a single column of the connectors  302  in the space between adjacent ones of the connectors  302 .  
     [0025] Alternatively, as illustrated in FIG. 5, the configuration of the connectors  302  yields diagonal paths that are substantially free of the connectors  302 . Thus, the capacitors  304  may be positioned diagonally in an end-to-end arrangement adjacent the connectors  300  that are coupled to receive the supply voltage. It should be appreciated that the configuration of the connectors  302  yields a second set of diagonal paths substantially perpendicular to the diagonal paths on which the capacitors  304  are located in FIG. 5. This second set of diagonal paths may be used instead of or in conjunction with the first set of diagonal paths.  
     [0026] Those skilled in the art will appreciate that the arrangements of the capacitors  304  illustrated in FIGS. 4 and 5 are not mutually exclusive. That is, the patterns shown in FIGS. 4 and 5 may be used conjointly to position a sufficient number and type of capacitors  304  adjacent each of the connectors  302  that are coupled to the power supply. More specifically, where useful, all of the patterns of the capacitors  304  discussed in conjunction with FIGS. 4 and 5 may be intermixed in a single application to provide adequate decoupling.  
     [0027]FIG. 6 illustrates a cross sectional view of the printed circuit board  202  in a region adjacent one of the capacitors  304 . The capacitor  304  may be mounted to the printed circuit board  202  using any of a variety of conventional techniques. For example, a chemical adhesive may be used to affix the body of the capacitor  304  to the printed circuit board  202 . The capacitor  304  may be coupled to the pads  306  using any of a variety of well-known techniques. For example, in the embodiment illustrated in FIG. 6, a pair of contacts  614  are formed on the body of the capacitor  304  and are coupled to the pads  306 . Typically, the contacts  614  are soldered to the pads  306 . In one embodiment, the pads  306  take the form of a via in pad (VIP), owing to space limitations.  
     [0028] As can be seen in the cross sectional view, the printed circuit board  202  includes at least two power planes (e.g., V cc  and ground)  600 ,  602 . A pad  604  associated with the semiconductor device  200  is electrically coupled to the first power plane  600  through a via  606 . Similarly, a second pad  608  associated with the semiconductor device  200  is electrically coupled to the second power plane  602  through a via  610 . The electrical connection between the pads  604 ,  608  and the power planes  600 ,  602  may be accomplished by any of a variety of conventional techniques. For example, the printed circuit board  202  may use the vias  606 ,  610  that are electrically coupled to the power planes  600 ,  602 . Integrally forming, soldering, or otherwise physically coupling the pads  604 ,  608  to these vias  606 ,  610  will connect the pads  604 ,  606  to the power planes  600 ,  602  as desired.  
     [0029] Those skilled in the art will appreciate that openings in the power planes  600 ,  602  permit the vias  606 ,  610  to pass therethrough without being directly electrically coupled thereto. Additionally, those skilled in the art will appreciate that where multiple voltage supplies are present, multiple power planes may also be used and decoupling capacitors may be positioned and connected to extend between the pads of the semiconductor device that are associated with these various multiple power planes to ensure adequate decoupling of each of the power supplies.  
     [0030] The particular embodiments disclosed above are illustrative only, as the invention may be modified and practiced in different but equivalent manners apparent to those skilled in the art having the benefit of the teachings herein. Furthermore, no limitations are intended to the details of construction or design herein shown, other than as described in the claims below. It is therefore evident that the particular embodiments disclosed above may be altered or modified and all such variations are considered within the scope of the invention. Accordingly, the protection sought herein is as set forth in the claims below.