Abstract:
A heat dissipation device includes a chip unit and a heat dissipation unit thermally attached to the chip unit. The chip unit includes a carrier substrate and a chip in electrical contact with the carrier substrate. The heat dissipation unit includes a heat spreader thermally contacting with the chip and a heat dissipation member coupled to the heat spreader. The heat spreader and the heat dissipation member are integrated together before they are attached to the chip unit.

Description:
FIELD OF THE INVENTION  
       [0001]     The present invention relates to a heat dissipation device, and more particularly relates to a heat dissipation device which has high heat dissipation efficiency and a method for making the same.  
       DESCRIPTION OF RELATED ART  
       [0002]     Higher performance, lower cost, increased miniaturization of electronic products, and greater packaging densities of integrated circuit are ongoing goals of the electronics industry. However, in achieving these goals, the heat produced by electronic components has also increased. If the temperature of the electronic component becomes too high, the electronic component may be damaged or destroyed. Thus it can be seen that advances in high science and technology have resulted in the temperature of the electronic component becoming a choke point. Therefore, designing heat dissipation devices with higher dissipation efficiency is an important challenge for the next generation of electronic products.  
         [0003]     Various apparatus and techniques are presently being used for removing heat from electronic products. One such heat dissipation device comprises a carrier substrate, a chip and a heat spreader. The chip is attached to one side of the carrier substrate, and a plurality of pins are located on the other side of the carrier substrate, connecting the chip to a printed circuit board (PCB). The heat spreader is located at the same side as the chip, positioned so as to absorb the heat generated by the chip. An interior surface of the heat spreader contacts a top surface of the chip with a layer of heat conduction material thereon. A heat dissipation member is attached to an exterior surface of the heat spreader. Thus a heat dissipation device is formed and a fan may be incorporated into the assembly to enhance the convective heat dissipation. The heat generated by the chip is dissipated into the air surrounding the heat dissipation device. However, the contact between the heat dissipation member and the heat spreader is not perfect and an air clearance may be formed, as put the heat dissipation member on the heat spreader directly. The air clearance greatly reduces the heat transfer from the electronic products, as be understood by those skilled in the art. A thermal interface material, for example grease, is applied to the surface of the heat spreader and within the clearance, to fill up the air clearance and to increase heat dissipation efficiency.  
         [0004]     Unfortunately, with the continuing development of electronics technology, the efficiency of heat removal is frequently not adequate for a modern electronic chip. The heat transfer coefficient of the thermal interface material, such as thermal grease is only about 2˜5 W/(m.K), that is much lower than most metals. Even if the heat dissipation capability of the heat dissipation member is improved along with increasing the airflow around the assembly, the improvement in the absolute total heat dissipation capability is limited.  
         [0005]     It is therefore desirable to provide a heat dissipation device capable of overcoming the above mentioned problems.  
       SUMMARY OF THE INVENTION  
       [0006]     A heat dissipation device according to a preferred embodiment of the present invention comprises a chip unit and a heat dissipation unit thermally attached to the chip unit. The chip unit comprises a carrier substrate and a chip electrically contacting the carrier substrate. The heat dissipation unit comprises a heat spreader thermally contacting the chip and a heat dissipation member coupled to the heat spreader. The heat spreader and the heat dissipation member are integrated together before they are attached to the chip unit. A hermetic space is formed between the heat spreader and the carrier substrate for receiving the chip.  
         [0007]     the advantages of this invention can be more readily ascertained from the following description of the invention when read in conjunction with the accompanying drawings, in which: 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0008]      FIG. 1  is a cross-sectional, assembled view of a heat dissipation device in accordance with a preferred embodiment of the present invention;  
         [0009]      FIG. 2  is a cross-sectional exploded view of the heat dissipation device of  FIG. 1 ;  
         [0010]      FIG. 3  is a cross-sectional assembled view of a heat dissipation device according to a second embodiment of the present invention; and  
         [0011]      FIG. 4  is a cross-sectional assembled view of a heat dissipation device according to a third embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0012]     Referring to  FIGS. 1-2 , the heat dissipation device comprises a chip unit  1  and a heat dissipation unit  2  thermally attached to the chip unit  1 . The chip unit  1  comprises a carrier substrate  20  and a chip  10  electrically contacting with the carrier substrate  20 . A plurality of solder balls  12  is electrically arranged between an interior surface of the carrier substrate  20  and a bottom surface of the chip  10 , thus electrically connecting the chip  10  with the carrier substrate  20 . A plurality of pins  22  are formed on an exterior surface of the substrate  20  for electrically connecting with a printed circuit board (PCB) (not shown). A layer of thermal interface material  40  is spread on a top surface of the chip  10 .  
         [0013]     The heat dissipation unit  2  comprises a heat spreader  30  and a heat dissipation member, such as a heat sink  50 . The heat spreader  30  may be constructed from a metallic material with a high heat transfer coefficient, such as copper, copper alloys, aluminum, aluminum alloys, and the like. In this embodiment, the heat spreader  30  is preferably made of copper. The heat spreader  30  comprises a cover portion  32  and a side portion  34  extending downwardly from a peripheral edge of the cover portion  32 . A space  36  is formed between the cover portion  32  and the side portion  34  for receiving the chip  10  therein. The layer of thermal interface material  40  is spread uniformly on the top surface of chip  10  and contacts the bottom surface of the cover portion  32 . The distal end of the side portion  34  hermetically connects to the interior surface of the substrate  20 . Thus the space  36  is hermetically formed between the cover portion  32 , the side portion  34  and the substrate  20  for hermetically enclosing the chip  10  therein.  
         [0014]     The heat sink  50  comprises a base  52  and a plurality of fins  54  extending from the base  52 . The base  52  steadily couples to the heat spreader  30  by soldering, sintering, or other known connection methods, such that the heat sink  50  and the heat spreader  30  are integrated together. The heat sink  50  and the heat spreader  30  are constructed from metallic material, such as copper and tungsten-copper alloys, of which the thermal transfer coefficients are 220 W/(m.K) and 398 W/(m.K) respectively. Thus a much better heat conduct surface between the heat spreader  30  and the heat dissipation member  50  is obtained, and the heat dissipation efficiency is increased.  
         [0015]     Amount of heat energy produced by the chip  10  reaches to the heat sink  50  through the conduction of the heat spreader  30 , and is further dissipated into the air surrounding the heat sink  50  fast. The heat dissipation efficiency is increased greatly, to ensure the chip  10  operates normally.  
         [0016]     Referring to  FIG. 3 , it can be seen that the heat spreader  230  and the heat sink  250  are integrally formed from a same metal stock, so as to completely avoid thermal resistance existing between contacting surfaces thereof.  
         [0017]     Referring to  FIG. 4 , the heat dissipation member  350  comprises a plurality of stacked fins  354  and a heat pipe  60  comprising an evaporation section  62  and a condensing section  64 . The evaporation section  62  contacts the heat spreader  330  horizontally, and the condensing section  64  extends through the fins  354  vertically. A groove (not labeled) is formed between the heat spreader  330  and the heat sink  350  for receiving the evaporation section  62  of the heat pipe  60 , and a through hole  358  is formed in each of the fins  354  for channeling the condensing section  64  of the heat pipe  60 . Preferably, the evaporation section  62  of the heat pipe  60  is soldered in the groove. Understandable, the groove may also be formed only in the heat spreader  330 , or in the heat sink  350  with the heat pipe  60  intimately contacting the heat spreader  330 . The heat produced by the chip  10  is transferred from the heat spreader  330  to the fins  354  by the heat pipe  60 , thus being further dissipated into the air surrounding the heat sink  350 . The fins  354  have larger heat dissipation area, and allow heat to be dissipated evenly and more efficiently. The number of the heat pipes  60  may be adjusted according to heat dissipation requirement. The evaporation section  62  of the heat pipe  60  has a flat configuration for enlarging the contacting area between the heat pipe  60  and the heat spreader  30 . The heat pipe  60  may be a loop-type heat pipe, of which one portion provides a flow-path for evaporated working fluid and the remaining portion provides a flow-path for condensed working fluid. The heat sink  350  is integrated to the heat spreader  330  by soldering or sintering before the heat spreader  330  is mounted to the carrier subsrate.  
         [0018]     In the above described embodiments, the heat dissipation member  50 ,  250 ,  350  and the heat spreader  30 ,  230 ,  330  are integrated together without thermal interface material, for example, thermal grease or thermal tape, being spread therebetween. Thus, high thermal resistance due to thermal interface material with low heat transfer coefficient being spread between the heat dissipation member and the heat spreader as in the conventional heat dissipation devices is avoided. The heat dissipation efficiency of the heat dissipation device of the present invention is thereby enhanced.  
         [0019]     In another aspect of the present invention, a method for making a heat dissipation device comprises the following steps: (1) providing the chip unit  1  and the heat dissipation unit  2 ; (2) Connecting the heat dissipation unit  2  to the chip unit  1 . In the step (1), the heat spreader  30 ,  330  and the heat sink  50 ,  350  of the heat dissipation unit  2  are integrated together by soldering or sintering, as show in the first and the third embodiments of the present invention. The heat spreader  230  and the heat sink  250  may be integrally formed by, for example, molding, as shown in the second embodiment of the present invention. The heat dissipation unit  2  may further comprises the heat pipe  60  (As show in  FIG. 4 ). In the step (2), the heat spreader  30  of the heat dissipation unit  2  is connected to the chip  10  by the layer of thermal interface material  40  applied uniformly onto the contacting surfaces. The heat dissipation unit  2  connects to the carrier substrate  20  by connecting the distal end of the side portion  34  of the heat spreader  30  to the carrier substrate  20  by soldering or gluing. The chip  10  electrically connects with the carrier substrate  20  by the plurality of solder balls  12 , and is hermetically enclosed by the heat spreader  30 .  
         [0020]     It is to be understood, however, that even though numerous characteristics and advantages of the present invention have been set forth in the foregoing description, together with details of the structure and function of the invention, the disclosure is illustrative only, and changes may be made in detail, especially in matters of shape, size, and arrangement of parts within the principles of the invention to the full extent indicated by the broad general meaning of the terms in which the appended claims are expressed.