Abstract:
A cooling device for a chip in a portable computer that uses a horizontal flat fan in the corner of a portable computer housing with air outlets through heatsinks that enhance exhaust air flow over heat pipes from the chip and out through the computer housing. The exhaust is through the adjacent vertical walls of the computer housing. Separate heat pipes go directly from the chip to fins located at the outlet at the wall.

Description:
FIELD OF THE INVENTION  
       [0001]     The invention is in the field of heat dissipation in portable electronic apparatus such as laptop computers where size, weight, and power consumption are constrained and in particular to heat transfer and cooling of heat produced in semiconductor chips used in such electronic apparatus.  
       BACKGROUND  
       [0002]     The power consumption of laptop computers, especially the power of Central Processing Units (CPUs) such as semiconductor chips used in them, is increasing. For instance, the total power of a laptop computer that was usually in the range of 10 watts, now is around 50 watts. The CPU power has been increased from 2 to about 18 watts and in the future it could reach 40 watts. Most of this power will be dissipated as heat to the surroundings. Getting more heat out of a laptop computer efficiently is becoming urgent.  
       RELATION TO THE PRIOR ART  
       [0003]     Although the idea of transferring heat from one place to another for dissipation is well known, the ability to transfer is constrained in the portable computer type of apparatus by the type of housing generally employed which is a shallow base with a hinged upper portion and by the air flow in that housing. There has been some work in the art as may be seen in the following documents.  
         [0004]     In U.S. Pat. No. 6,105,662, titled “Cooling System for Electronic Packages”, there is taught a cooling system including a heat radiator or heat sink connected to a heat conducting plate by means of a particular tube-like heat conducting element for heat transfer.  
         [0005]     In U.S. Pat. No. 6,111,748, titled “Flat Fan Heat Exchanger and Use Thereof in a Computing Device”, there is taught a fan heat exchanger including one type of flat fan that has air coming in from one side and exiting to the opposite side of the fan housing at the same level. The patent shows several fan types in moving air guided with fins, in a typical computer housing.  
         [0006]     There is developing a need in the art to move larger amounts of air in order to carry the ever increasing heat from the CPU chip or chips to the outside of the computer housing.  
       SUMMARY OF THE INVENTION  
       [0007]     A cooling device for a portable computer is provided that uses a flat fan having air inlet capability into the fan housing near the propeller shaft of the fan and having dual air outlets through the fan housing, in combination with dual finned heat sink exhaust air outlets through the computer housing. Each exhaust air outlet through the computer housing being independently connected via a separate heat pipe to the relatively physically small heat source of the computer such as a semiconductor chip. The air outlets and heat sinks exhaust through the adjacent vertical walls of the computer housing producing a situation where input air comes into the fan housing parallel to, and exits perpendicular to,the shaft or axis of the fan. Each air outlet heatsink combination is provided with fins that together with position enhance volume of air flow. The heat from the chip is thus conveyed for transfer into the exhaust air at the exit point from the computer housing.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0008]      FIG. 1  is a perspective depiction of the elements of the invention positioned at an intersection of housing walls in a laptop computer.  
         [0009]      FIG. 2  is a top view of the flat fan assembly combined with the finned heatsink air outlets.  
         [0010]      FIG. 3  is a cross-sectional view of the flat fan of the invention illustrating the air inlets and air outlets.  
         [0011]      FIGS. 4   a  and  4   b  are top and side view depictions respectively for an end of a heat pipe passing through a fin assembly.  
         [0012]      FIG. 5  is a side view depiction of the assembly of the separate heat pipes in contact with a single heat generating source such as a semiconductor chip on a printed-wiring board.  
         [0013]      FIG. 6  is a perspective depiction of connection blocks use in retaining an end of a heat pipe. 
     
    
     DESCRIPTION OF THE INVENTION  
       [0014]     Referring to  FIG. 1 a  perspective depiction is provided of the elements of the invention positioned at an intersection of housing walls in a laptop computer and to  FIG. 2  which is a top view of the flat fan assembly combined with the finned heatsink air outlets. The base  1  of the computer has intersecting walls  2  and  3  and a hinged display member  4 .  
         [0015]     The flat fan assembly  5  is in a horizontal position at the intersection of the walls  2  and  3 . The assembly  5  has air inlets  6  A on the upper side, which is shown removed in  FIG. 2 , and  6 B on the lower side. The flat fan assembly  5  further has air outlet regions  7  A and  7 B that are not visible in  FIG. 1 , and are separated around the periphery of the fan assembly  5  in  FIG. 2 . The regions  7 A and  7 B are each in a combination with air flow enhanced heat sink members  8  and  9 , and in turn are each independently connected via separate heat pipes  10  and  11  to a physically small heat source  12  such as a semiconductor chip, located under the ends of the heat pipes  13  and  14  not visible in this figure, and mounted on a substrate board  15 . The air inlets  6 A and  6 B, are near the axis  16  of the fan assembly  5 . The structure of FIGS.  1  and  FIG. 2  produce a situation where input air comes into the fan assembly  5  parallel to, and exits perpendicular to, the axis  16  of the fan.  
         [0016]     Each heatsink member  8  and  9  is provided with fins that enhance air flow. The fins are not visible in  FIG. 1  and are labelled  40  and  41  in  FIG. 2 . The heat is conveyed through the separate heat pipes  10  and  11  from the chip  12  to the separate heatsinks  8  and  9  so that the heat pipes  10  and  11  each transfers all heat at the exit,  40  through wall  3 ,  41  through wall  2 , of the computer housing. A clamping mechanism  18  in  FIG. 1  is used to hold the two heat pipe ends  13  and  14  in good thermal contact with the chip package. The structural details of the compact cooling device are further shown in  FIG. 2  which is a top view of the flat fan assembly  5  in combination with the finned heatsink air outlets  8  and  9 . Considering the structure and operation of the invention in  FIG. 2 , which is the flat fan housing  5  of  FIG. 1  with the cover containing air inlets  6 A removed permitting viewing inlets  6 B.  
         [0017]     The housing  5  has portions  21  and  21 A that hold the parts containing the air inlets  6 A and  6 B apart and define the air outlet openings  7 A and  7 B. The shaft  23  holds the fan motor  22 , not shown. Numerous fan blades  24  are attached to the shaft  23 . With counter clockwise rotatation the outgoing air, as indicated by the arrows labelled  25  moves at higher volume where the air outlet heatsinks  8  and  9  are at less than the right angle of the computer housing walls  2  and  3 .  
         [0018]     It will be apparent that the shape of the fan housing  5 , the number of the fan blades  24 , and the number of openings at the air inlets  6 A and  6 B are exemplary and should not be limited to those shown in the figure. The construction of the fins  40  and  41  of the invention are arranged for maximum air flow volume enhancement, they vary in length and distance apart and the fin assemblies depart from being perpendicular to the sides  2  and  3  in the direction of tangency to the air flow  25  direction in the fan.  
         [0019]     Referring to  FIG. 3  where the fan in the housing  5  of  FIGS. 1 and 2  is shown in cross section in  FIG. 3 . along the dotted line  3 - 3  in  FIG. 2 . The motor and motor shaft  23  is in the center. The majority of the electronics to drive the motor is associated with the shaft  23 . The air inlets  6 A are through the upper cover and the air inlets  6 B are through the lower cover. The air outlets  27  and  28  direct air output through to the heatsinks  8  and  9  as directed by elements  21  and  21 A, out of view in  FIG. 3 .  
         [0020]     Referring to  FIG. 4  there are side and top view depictions labelled  FIGS. 4A and 4B  respectively showing the end of the heat pipe  11  shown dotted in  FIG. 2 , passing through the fin assembly  40  of heatsink  8 . The structure of the two air heatsink outlets  8  and  9  are identical in principle as depicted in  FIG. 2 . As indicated in the side view of the air outlet heatsink  8  in  FIG. 4   a,  one end of the heat pipe  11  is inserted at its main body with numerous fins  40  protruded outward. The air outlet heatsink  8  and its fins  40  are made of thermally conductive materials such as aluminum or copper. A cover  45  surrounding the fins  40  to protect the fins and guide the air flow may be provided. As illustrated in  FIG. 4B  the spacing  46  between the fins varies according to the length of the fins. Further, as illustrated in both  FIG. 2  and  FIG. 4  the fin length varies to conform with the shape of the fan outlet  27 .  
         [0021]     Referring to  FIG. 5  there is shown a side view of the clamping mechanism to bring the heat pipes in contact with the heat generating semiconductor chip  12 . The semiconductor chip  12  is soldered on a printed-wiring board  52 . The two connection blocks  13  and  14  with heat pipes  10  and  11  inserted within are placed on the top of the semiconductor chip  12 . The connection blocks are forced into a good thermal contact with the chip  12  by two elastomer or spring pieces  50  using a clamp  51  which is anchored on the printed-wiring board  52 .  
         [0022]     The heat pipe structures lend themselves to variety of arrangements. As shown in  FIG. 6 , the connection block  55  consists of two pieces. One end of the connection block piece has a trough-like cut  56 . The heat pipe  10  is inserted into the two connection block pieces with the trough-like cuts facing each other. The two connection block pieces are separated by a clearance  57 . The dimension of the trough-like cut is made larger than the diameter of the heat pipe such that there is a free space  58  under and around the heat pipe within the cut  56 . The two connection block pieces pick up the heat from the semiconductor chip and conduct it to the heat pipe. This two-piece structure of the connection block provides a certain degree of the freedom for the connection blocks to make a compliant contact with the surface of the semiconductor chip. A reliable and efficient thermal contact is therefore ensured. The thermal contact can be improved further if the spaces between the block pieces and the spaces within the trough-like cut in the block pieces are filled with thermally conductive fluid-like or gel-like materials such as thermal pastes.  
         [0023]     What has been described is device principle for heat dissipation in portable electronic apparatus such as laptop computers where size, weight, and power consumption are constrained.