Abstract:
A spring plate may be provided between a bolster plate and a board in order to mount components on the opposite side of the board. In some embodiments, the spring plate may provide additional stack tolerance and forceful bias to hold the stack tightly together.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   This application is a divisional of U.S. patent application Ser. No. 10/844,765, filed on May 13, 2004 now U.S. Pat No. 6,992,373. 

   BACKGROUND 
   This invention relates generally to packaging integrated circuits. 
   Integrated circuits, such as microprocessors, may be packaged in various configurations. One such configuration is called a land grid array package. With land grid array packaging, integrated circuit die may be coupled to circuit boards through sockets that electrically and mechanically couple the integrated circuit die to the circuit board. In some cases, the connection may be via socket spring fingers which contact lands on the integrated circuit packages to make a land grid array connection system. 
   Often, a number of components may be connected together to form a stack. In one example a voltage regulator module board may be assembled on a motherboard through a land grid array connector. The voltage regulator module and motherboard are clamped together between a bolster plate under the motherboard. A heat sink may be positioned on top of the voltage regulator module board. Pairs of standoffs on the bolster plate are used to control the space in between the bolster plate and the heat sink. 
   Due to the dimensional tolerances of the mechanical parts, the distance between the bolster plate and the heat sink varies on individual assembly. Part of this stack tolerance can be absorbed by the flexibility of the land grid array springs. However, the bending range of land grid array springs is limited and cannot absorb the entire stack tolerance. 
   In the meantime, a certain level of pressure is required to press the land grid array onto the land pads on the motherboard to meet the requirement of good electrical design. 
   Thus, there is a need for better ways to connect integrated circuits to boards in the form of stacks. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is an enlarged, cross-sectional view through one embodiment of the present invention; 
       FIG. 2  is a cross-sectional view taken generally along the line  2 — 2  in  FIG. 1 ; 
       FIG. 3  is a perspective view of a spring plate in accordance with one embodiment of the present invention; 
       FIG. 4  is a perspective view of a spring plate in accordance with another embodiment of the present invention; and 
       FIG. 5  is a system schematic according to one embodiment of the present invention. 
   

   DETAILED DESCRIPTION 
   Referring to  FIG. 1 , a land grid array package stack  10  may include a voltage regulator module heat sink  12  mounted on a voltage regulator module board  14 . Under the board  14  may be a voltage regulator module socket or connector  16 . The connector  16  may be positioned over a motherboard  18  which, in turn, is positioned over an insulator  20  in one embodiment. The board  14 , connector  16 , board  18 , and insulator  20  may be mounted on a set of standoffs  30  which allow relative vertical movement of the stack  10  while controlling the side to side or lateral movement thereof. A screw  50 , in turn, is connected through the standoffs  30  to a bolster plate  22  on the bottom of the stack  10  to hold the stack  10  together. Between the bolster plate  22  and the board  18  is positioned a spring plate  24 . 
   In some embodiments, the spring plate  24  provides the required pressing load on the back of the board  18  and thereafter on the land grid array connector  16 , while absorbing the stack tolerance. As mentioned above, due to the dimensional tolerance of the mechanical parts, the distance between the bolster plate  22  and the heat sink  12  may vary on individual assembly. While part of this tolerance can be absorbed by the flexibility of the land grid array connector springs, the entire tolerance cannot be so absorbed. Thus, the spring plate  24  may function to absorb that tolerance. In some embodiments, the spring plate can supply a recovery force while reducing or even minimizing the tilting or uneven contact of the land grid array connector  16  on the board  18 . 
   To this end, the spring plate  24  may include two or more pairs of independent spring legs  32  as shown in  FIG. 2 . The spring plate  24  may be formed of stamped metal in one embodiment of the present invention. For example, the spring plate  24  may be made of BeCu alloy which has a lower Young&#39;s modulus and a higher yield strength than steel. 
   A set of four spring legs  32  may be positioned on the center bar  34  of the spring plate  24  in one embodiment. The spring legs  32  may be partially cut out of the rest of the plate  24  and may be bent upwardly, towards the board  18 , as the spring legs extend away from the center bar  34 . The free ends  40  of the spring legs  32  may be bent over to prevent gouging of the mating surfaces. The span in the spring legs  32  may be less than half of the plate  24  width in some embodiments. 
   Clips  26  and  28  may be provided to ease assembly. For example, in one embodiment, the clips  28  extend downwardly from one half of the plate  24  while the clips  26  extend upwardly from the other half of the plate  24 , as shown in  FIG. 3 . In other words, the clips  26  may engage the sides of the board  18  while the clips  28  engage the sides of the bolster plate  22  in one embodiment. The center bar  34  may include U-shaped openings  42  to receive the standoffs  30  in one embodiment of the present invention. 
   In some embodiments of the present invention, the spring plate  24  provides a low profile spring to absorb the stack tolerance while maintaining the desired pressure force in a limited space. 
   The spring legs  32  may be made by cutting and forming sheet metal in one embodiment of the present invention. For example, stamping may be utilized for this purpose. 
   The free ends  40  of the spring legs  32  are closer to the edges of the plate  24 , while the lower ends sit closer to the plate center bar  34 . The free ends  40  contact the object being supported. Larger spacing may be achieved between the free ends  40  due to this configuration which can supply a recovery force to reduce or minimize the tilting of the connector  16  relative to the board  18 . 
   The height of the free ends  40  depends on the application and may be minimized to maintain a low profile in some embodiments. The free state height can be no larger than 10 percent of the plate  24  width in one embodiment of the present invention. The preload height can be less than one millimeter in one embodiment of the present invention. The use of the rounded free ends  40  may avoid any concentrated contact and scratching of other components in some embodiments. 
   The spring plate  24  uses a closed design as shown in  FIG. 3  with turned free ends  40 . The arms  32  may be straight as shown in  FIG. 3 . The plate  24  may provide better structural integrity in some embodiments. 
   Alternatively, an opened design may be utilized in the plate  24   a  as shown in  FIG. 4 . In the opened design, there are no turned over free ends  40 . In addition, the arms  32  may be curved. The opened design may provide for more flexibility in some embodiments. 
   In one embodiment of the present invention, the length of each spring leg  32  may be 16 millimeters and the span of the spring leg may be 4 millimeters. The free state height of the raised end  40  may be 1.5 millimeters with a plate thickness of 0.4 millimeters in such an embodiment. Such a structure can absorb a working stack tolerance range of about 0.6 millimeters, while maintaining the total pressing force at greater than 40 pounds. 
   Referring to  FIG. 5 , in accordance with one embodiment of the present invention, a system  50  may be implemented by a motherboard  18  and a voltage regulator module board  14 . The motherboard  18  may include a processor  52 , a system memory  56 , and a bus  54 . The connector  16  couples the voltage regulator module  58  to the bus  54 . While  FIG. 5  shows one system implementation of the present invention, those skilled in the art will appreciate that the present invention is in no way limited to any particular system implementation. 
   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.