Patent Publication Number: US-2006002091-A1

Title: Micro heat spreader

Description:
BACKGROUND OF THE INVENTION  
      1. Field of the Invention  
      The present invention relates to a micro heat spreader for use with a semiconductor chip to spread heat.  
      2. Description of the Related Art:  
      Following fast development of nanotechnology, the number of transistors in an IC chip has been increased in the manner of geometric progression. A high-density IC chip provides a strong operating power. However, a high-density IC chip releases much heat during operation. Various heat dissipation devices have been disclosed to dissipate heat from a semiconductor chip. A micro heat spreader or the so-called flat thermal tube is one of the most efficient heat dissipation devices for this purpose. Conventional micro heat spreaders commonly comprise a flat panel, which defines therein a vacuum chamber, and a fluid filled in the vacuum chamber for spreading heat energy. A regular micro heat spreader further comprises a filling hole in one side wall in fluid communication with the vacuum chamber. During fabrication, a copper tube is inserted into the filling hole for drawing air out of the vacuum chamber. After filling of the fluid into the vacuum chamber, the copper tube is properly cut and sealed by arc welding. After arc welding, the welded outer end of the copper tube protrudes over the outside wall of the micro heat spreader at a distance about 5 mm. The protruded outer end of the copper tube hinders the installation of the micro heat spreader in an electronic package.  
      There is known another design of micro heat spreader, which has the filling hole formed in the bottom wall. After arc welding to seal the outer end of the copper tube that is inserted into the filling hole for drawing air out of the vacuum chamber, the protruded outer end of the copper tube hinders close attachment of the micro heat spreader to a semiconductor chip, thereby lowering the heat spreading efficiency of the micro heat spreader.  
     SUMMARY OF THE INVENTION  
      The present invention has been accomplished under the circumstances in view. It is one object of the present invention to provide a micro heat spreader, which has a flat bottom wall that can be closely attached to a semiconductor chip close. It is another object of the present invention to provide a micro heat spreader, which effectively spreads heat during operation of the semiconductor chip to which the micro heat spreader is attached. To achieve these and other objects of the present invention, the micro heat spreader comprises an inside vacuum chamber, a bottom recess in the bottom wall thereof, a filling hole formed in the bottom recess in fluid communication with the inside vacuum chamber, a fluid filled into the inside vacuum chamber, and a bronze stopper fastened to the bottom recess to seal the filling hole and maintained in flush with the bottom wall. Alternatively, a metal tube may be used and mounted in the filling hole to substitute for the bronze stopper. After filling of the fluid into the vacuum chamber, the outer end of the metal tube is properly cut and hammered down to close the passage of the filling hole, keeping the closed outer end of the metal tube inside the bottom recess of the micro heat spreader without hindering the installation of the micro heat spreader in a semiconductor chip. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1 ( a ) is an oblique bottom elevation of a micro heat spreader according to the first embodiment of the present invention.  
       FIG. 1 ( b ) is a side view in section of the micro heat spreader according to the first embodiment of the present invention.  
       FIG. 2 ( a ) is an oblique bottom elevation of a micro heat spreader according to the second embodiment of the present invention.  
       FIG. 2 ( b ) is a side view in section of the micro heat spreader according to the second embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
      Referring to FIGS.  1 ( a ) and  1 ( b ), a micro heat spreader  20  in accordance with the first embodiment of the present invention is shown comprising an inside vacuum chamber  22 , a circular recess  26  formed in the bottom wall, a filling hole  24  formed in the circular recess  26  in fluid communication with the inside vacuum chamber  22 , and a stopper  40  fitted into the circular recess  26  to seal the filling hole  24 .  
      During fabrication of the micro heat spreader  20 , vacuum pump means (not shown) is attached to the circular recess  25  and the filling hole  24  to draw air out of the inside vacuum chamber  22 . After the inside vacuum chamber  22  has been changed into a vacuum status, a fluid or water is filled through the filling hole  24  into the inside vacuum chamber  22 , and then the stopper  40  is fastened to the circular recess  26  to seal the filling hole  24 . According to this first embodiment, the stopper  40  is a bronze member spot-welded to the circular recess  25  of the micro heat spreader  20  and maintained in flush with the bottom wall of the micro heat spreader  20 .  FIG. 1 ( b ) shows the micro heat spreader  20  attached to a semiconductor chip  44 . Because the stopper  40  is kept in flush with the bottom wall of the micro heat spreader  20 , the micro heat spreader  20  can be maintained closely attached to the semiconductor chip  44 . Further, the micro heat spreader  20  is fixedly secured to the semiconductor chip  44  by an adhesive by means of the application of an adhesive machine.  
      FIGS.  2 ( a ) and  2 ( b ) show a micro heat spreader constructed according to a second embodiment of the present invention. According to this embodiment, the micro heat spreader  20  comprises an inside vacuum chamber  22 , a bottom recess  28  formed in the bottom wall, a filling hole  24  formed in the bottom recess  28  in fluid communication with the inside vacuum chamber  22 , and a copper tube  42  inserted into the filling hole  24 . The bottom recess  28  has a substantially U-shaped profile. The protruding outer end of the copper tube  42  is properly cut and hammered down to close the passage of the filling hole  24  after the inside vacuum chamber  22  has been processed into a vacuum status and filled with a fluid. After fabrication, the closed outer end of the copper tube  42  is kept inside the bottom recess  28  and spaced from the bottom wall of the micro heat spreader  20  at a distance. Therefore, the closed outer end of the copper tube  42  does not hinder the installation of the micro heat spreader  20  in a semiconductor chip  44 .  
      A prototype of micro heat spreader has been constructed with the features of  FIGS. 1 and 2 . The micro heat spreader functions smoothly to provide all of the features discussed earlier.  
      Although particular embodiment of the invention have been described in detail for purposes of illustration, various modifications and enhancements may be made without departing from the spirit and scope of the invention.