Patent Publication Number: US-2006014323-A1

Title: Thermal interface material with fluid

Description:
FIELD OF THE INVENTION  
      The present invention relates to thermal interface materials, such as a thermal interface material positioned between a heat sink and a heat source.  
     BACKGROUND OF THE INVENTION  
      Nowadays semiconductor devices are smaller and run faster than ever before. These devices also generate more heat than ever before. A semiconductor device should be kept within its operational temperature limits to ensure good performance and reliability. Referring to  FIG. 3 , to keep a semiconductor device  70  in its operational temperature range, a heat sink  60  is attached to a surface of the semiconductor device  70 . Heat is transferred from the semiconductor device  70  to ambient air via the heat sink  60 . When the heat sink  60  is attached to the semiconductor device  70 , their surfaces are adjacent to each other. However, as much as 99% of the surfaces are actually separated by a small layer of interstitial air  90 , no matter how precisely the heat sink  60  and semiconductor device  70  are manufactured.  
      Referring to  FIG. 4 , a thermal interface material  50  can be positioned in a region of interstitial air between a heat sink  62  and a semiconductor device  72 . The thermal interface material  50  is mobile over the semiconductor device  72 , thereby filling the space between the heat sink  62  and the semiconductor device  72 . However, the viscosity of the thermal interface material  50  limits its spreadability, so that the space  92  between the heat sink  62  and the semiconductor device  72  cannot be fully filled. Thus air remains in unfilled portions of the space  92 , which increases the thermal resistance between the heat sink  62  and the semiconductor device  72 .  
      Thus, an interface material which overcomes the above-mentioned problems is desired.  
     SUMMARY  
      Accordingly, an object of the present invention is to provide an interface material filling a gap between a heat sink and a heat source for facilitating heat transfer from the heat source.  
      To achieve the above-mentioned object, a thermal interface material is provided to insert into a gap between a heat sink and a heat source in order to dissipate heat from the heat source. The gap has air therein. The thermal interface material may include a fluid and a number of metal particles in the fluid. The metal particles may react with the air to form one or metal compounds at least partly filling the gap. The reaction reduces the amount of air between the heat sink and the heat source, thereby decreasing the thermal resistance between the heat sink and the heat source.  
      Preferably, the metal particles are made of a metallic material selected from the group consisting of aluminum, magnesium, and iron. The metal compounds may be metal oxides. The metal compounds may be metal nitrides.  
      The metal oxides and metal nitrides may be provided to replace the amount of air between the heat sink and the heat source. Because the metal oxides and metal nitrides conduct heat better than the amount of air, the efficiency of the thermal conduction between the heat sink and the heat source is increased by this replacement.  
      Other advantages and novel features will be drawn from the following detailed description of preferred embodiments together with the attached drawings, in which: 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  is a schematic view of a heat dissipating assembly, showing a thermal interface material of the present invention positioned between a heat sink and a heat source before the interface material reacts with air;  
       FIG. 2  is similar to FIG  1 , but showing the assembly after the interface material has reacted with air;  
       FIG. 3  is a schematic view of a conventional assembly including a heat sink and a semiconductor device; and  
       FIG. 4  is similar to  FIG. 3 , but showing a conventional thermal interface material positioned between a heat sink and a semiconductor device. 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS  
      In one aspect, the present invention provides a thermal interface material for filling a gap between two thermal objects, of which a first thermal object is exemplarily a heat sink and a second thermal object is exemplarily a heat source, and thereby facilitating transfer of heat from the heat source to the heat sink. Referring to  FIGS. 1 and 2 , the heat source  30  and the heat sink  20  are partially separated by a gap  49  having air  51  therein. The thermal interface material  10  includes a fluid  12 , and a number of metal particles  11  distributed in the fluid  12 . The metal particles  11  react with the air  51  to form one or more metal compounds  13 , whereby the thermal interface material  10  substantially fully fills the gap  49  between the heat sink  20  and the heat source  30 .  
      The metal particles  11  are made of a metallic material that can readily chemically react with the air  51 . Such metallic material may be aluminum, magnesium, iron, or any combination thereof. Each of the metal particles  11  may have a diameter in the range from about 1 to about 100 nanometers. The metal particles  11  are added into the fluid  12 , and subsequently react with the air  51  to form the metal compounds  13  that fills up the gap  49  between the heat sink  20  and the heat source  30 . The metal compounds  13  include metal oxides and metal nitrides. The fluid  12  is selected from the group consisting of oil, grease, and a colloid. The oil is preferably mineral oil, silicon oil, petroleum jelly, or Vaseline™. The grease is preferably animal grease or plant grease. The colloid is preferably silica gel, polyethylene glycol, epoxy resin or an acrylic.  
      Referring back to  FIG. 1 , the thermal interface material  10  is positioned between the heat source  30  (e.g., a CPU—central processing unit) and the heat sink  20 . The fluid  12  of the thermal interface material  10  is mobile, thereby filling the gap  49  between the heat sink  20  and the heat source  30 . Even if the fluid  12  cannot fully fill the gap  49 , the metal particles  11  in the fluid  12  are chemically reactive enough to react with the air  51  between the heat sink  20  and the heat source  30 . The product of the reaction is the metal compounds  13  (see  FIG. 2 ), which reduce or eliminate the air  51  between the heat sink  20  and the heat source  30 .  
      Referring to  FIG. 2 , the metal compounds  13  and the fluid  12  may substantially fill up the space between the heat sink  20  and the heat source  30 . That is, the thermal interface material  10  closely attaches the heat sink  20  to the heat source  30 , thereby providing intimate thermal contact between the heat sink  20  to the heat source  30 .  
      The previously described aspects of the present invention have many advantages. First, the metal particles are chemically reactive enough to react with the air. Approximately eighty percent of air is nitrogen, and approximately twenty percent of air is oxygen. The nitrogen reacts with the metal particles to form metal nitrides. The oxygen reacts with the metal particles to form metal oxides. These reactions reduce the amount of air between the heat sink and the heat source, thereby decreasing the thermal resistance between the heat sink and the heat source. From another point of view, the metal oxides and metal nitrides are formed to replace the amount of air between the heat sink and the heat source. Because the metal oxides and metal nitrides conduct heat better than the amount of air, the efficiency of the thermal conduction between the heat sink and the heat source is increased by this replacement.  
      Second, each of the metal particles preferably has a diameter in the range from about 1 to about 100 nanometers. Therefore the metal particles have a large surface area. This large surface area increases the reaction rates, thereby effectively reducing or eliminating the air between the heat sink and the heat source. This increases the efficacy of the thermal interface material.  
      It is understood that the above-described embodiments are intended to illustrate rather than limit the invention. Variations may be made to the embodiments without departing from the spirit of the invention. Accordingly, it is appropriate that the appended claims be construed broadly and in a manner consistent with the scope of the invention.