Patent Document

[0001]     This application is a Division of co-pending application Ser. No. 10/339,488, filed on Jan. 10, 2003, the entire contents of which are hereby incorporated by reference and for which priority is claimed under 35 U.S.C. §120. 
     
    
     FIELD OF INVENTION  
       [0002]     The invention relates to a heat sink and, in particular to a heat sink with a heat dissipating base that has a three-dimensional curved surface.  
       Related Art  
       [0003]     With the increasing efficiency of electronic devices, the heat dissipating device or system becomes indispensable equipment. If the heat produced by an electronic device is not released to the environment properly, the efficiency may deteriorate or the device may burn out. Therefore, the heat dissipating device is of particular importance to microelectronic devices (e.g. IC). With the increase in the density of elements and advance in the packaging technology, the IC&#39;s have even smaller areas. At the same time, the heat accumulated in each unit area grows. Therefore, highly efficient heat sinks always form an important research subject in the electronics industry.  
         [0004]     Generally speaking, the heat dissipating device is installed on the surface of a heat-generating device to remove the heat form the device. According to the shape of the base, the heat dissipating devices can be categorized as planar and cylindrical ones.  
         [0005]     Please refer to  FIGS. 1, 2  and  3 .  FIG. 1  is a schematic view of the conventional heat dissipating device  10 .  FIG. 2  is a top view of the planar heat sink  20  shown in  FIG. 1 .  FIG. 3  is a side view of the planar heat sink  20  along the  3 - 3  cross section. As shown in these drawings, the heat dissipating device  10  includes an axial-flow fan  12  and a planar heat sink  20 . The planar heat sink  20  has a copper or copper alloy heat conductive plate  24 , an aluminum or aluminum alloy heat dissipating shell  26  covering over the heat conductive plate  24 , and a plurality of aluminum or aluminum alloy heat dissipating fins  22  perpendicularly installed on the heat dissipating shell  26 . The fan  12  is embedded and fixed on the fins  22  of the heat sink  20 . The lower surface of the heat conductive plate  24  is attached onto a heat-producing device (e.g. a CPU, not shown in the drawing).  
         [0006]     The heat-producing device releases a lot of heat during operations. Since copper has an extremely good heat conductive property, the released heat rapidly flows toward the heat dissipating shell  26  and to the fins  22  through the heat conductive plate  24 . The fan  12  further blows the heat on the fins  22  away, thereby achieving the heat dissipation effect. However, the produced heat forms a heat flow field (see  FIG. 3 ) within the heat conductive plate  24 . This results in a worse heat conductive effect in the central area of the base  24 . Moreover, the position that generates the most heat in a typical heat-producing device is the central region. Therefore, the central area of the heat conductive plate  24  in the planar heat sink  20  requires a better heat conducting element to enhance the dissipation effect.  
         [0007]     To improve the heat dissipation effect in the central region of the heat conductive plate  24 , a cylindrical heat sink is proposed in the prior art. Please refer to  FIGS. 4, 5  and  6 .  FIG. 4  shows another conventional heat dissipating device  30 .  FIG. 5  is a top view of the cylindrical heat sink  40  in  FIG. 4 .  FIG. 6  is a side view of the cylindrical heat sink  40  along the  6 - 6  cross section. As shown in the drawings, the heat dissipating device  30  contains an axial-flow fan  12  (same as in  FIG. 1 ) and a cylindrical heat sink  40 . The cylindrical heat sink  40  is comprised of a copper or copper alloy heat conductive cylinder  44 , an aluminum or aluminum alloy heat dissipating shell  46  covering over the rim of the heat conductive cylinder  44 , and a plurality of aluminum or aluminum alloy fins  42  perpendicularly installed on the shell  46 . Analogously, the fan  12  is embedded and fixed on the fins  42  of the heat sink  40 . The other surface of the heat sink  40  is then attached onto the heat-producing device (e.g. CPU).  
         [0008]     As the heat-producing device is in direct contact with the heat sink surface  40 , the heat released during the operation of the heat-producing device quickly flows to the heat conductive cylinder  44 , the heat dissipating shell  46 , and the fins  42 . Through the cylindrical design, the heat flows along the heat conductive cylinder  44 , the shell  46 , and the fins  42  in the axial direction toward to fan  12 . The fan then provides air convection to bring out the heat.  
         [0009]     From the above description, one sees that the cylindrical heat sink  40  indeed solves the unsatisfactory heat dissipation effect in the central region of the planar heat sink  20 . However, it is easily seen from the heat flow field in  FIG. 6  that the region close to the connection interface between the heat sink  40  and the fan  12  does not have a good dissipation effect. This obviously is a waste of available space in the heat dissipating device  30 . It is very unpractical to use such devices in small electronics.  
         [0010]     Furthermore, the heat conductive plate  24  of the heat sink  20  and the heat conductive cylinder  44  of the heat sink  40  are connected to the heat dissipating shell  26 ,  46  by soldering, bonding, or high-pressure mounting, respectively. If the precision of the heat conductive plate  24 , he heat conductive cylinder  44 , and the heat sinks  26 ,  46  is not high enough, air gaps may appear at the connection interfaces. Besides, soldering often increases the thermal resistance of the contact interface, also affecting the heat conduction effect of the heat sinks  20 ,  40 .  
       SUMMARY OF THE INVENTION  
       [0011]     The invention provides an improved heat sink with a heat dissipating base that has a three-dimensional curved surface. By tight connection between the heat dissipating base and the heat dissipating shell using the disclosed connector, an optimal heat conduction effect can be achieved. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]     The invention will become more fully understood from the detailed description given hereinbelow illustration only, and thus are not limitative of the present invention, and wherein:  
         [0013]      FIG. 1  is the schematic view of a conventional heat dissipating device;  
         [0014]      FIG. 2  is a top view of the planar heat sink in  FIG. 1 ;  
         [0015]      FIG. 3  is a side view of the planar heat sink along the cross section  3 - 3 ;  
         [0016]      FIG. 4  is the schematic view of another conventional heat dissipating device;  
         [0017]      FIG. 5  is a top view of the cylindrical heat sink in  FIG. 4 ;  
         [0018]      FIG. 6  is a side view of the cylindrical heat sink along the cross section  6 - 6 ;  
         [0019]      FIG. 7  is a schematic view of the disclosed heat dissipating device;  
         [0020]      FIG. 8  is a top view of the heat sink in the first embodiment of the invention;  
         [0021]      FIG. 9  is a side view of the heat sink in  FIG. 8  along the cross section  9 - 9 ;  
         [0022]      FIG. 10A  shows the thermal resistance of the heat dissipating base as a function of the ratio of the cross section width of the bottom surface of the heat conductive block and the cross section width of the heat conductive plate in the first embodiment of the invention;  
         [0023]      FIG. 10B  shows the thermal resistance of the heat dissipating base as a function of the ratio of the vertical height of the heat dissipating base and the vertical height between the lower surface of the heat dissipating base and the top of fins in the first embodiment;  
         [0024]      FIG. 10C  shows the thermal resistance of the heat dissipating base as a function of the angle subtended between the bottom surface and the side surface of the heat conductive block in the first embodiment;  
         [0025]      FIG. 11  is a side view of the heat sink in the second embodiment along the cross section  11 - 11 ; and  
         [0026]      FIG. 12  is a side view of the heat sink in the third embodiment along the cross section  12 - 12 .  
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0027]     The disclosed heat sink is mounted on a heat-producing device, which can be a microprocessor or a central processing unit (CPU). As shown in  FIGS. 7, 8  and  9 , the heat dissipating device  50  of the invention contains an axial-flow fan  12  and a first improved heat sink  60 . The heat sink  60  contains a heat dissipating base  70  with a three-dimensional curved surface and a plurality of heat dissipating fins  62 . The base  70  contains a heat conductive plate  64  and a heat conductive block  66  installed at the center of the topmost surface  61  of the heat conductive plate  64 . The fins  62  are mounted perpendicular to the topmost surface  61  of the heat conductive plate  64  and the side surface  68  of the heat conductive block  66 . Since the fins  62  are installed along the side surface  68 , they have different surface areas. The fan  12  can be fixed onto the heat sink  60  using four fixing elements (e.g. screws) on the fins  62  at the four corners.  
         [0028]     It should be emphasized that the heat sink  60  in the first embodiment is featured in that: the heat conductive plate  64  of the heat dissipating base  70  is installed with an approximately cylindrical heat conductive block  66  on the top surface  61 . That is, the bottom surface area of the block  66  is greater than its topmost surface area. The heat conductive block  66  and the heat conductive plate  64  are formed together using aluminum, aluminum alloys, copper, copper alloys that have high coefficient of thermal conduction to form a heat dissipating base  70  with a three-dimensional curved surface. The fins  62  on the heat dissipating base  70  are soldered or formed together with the heat dissipating base  70 .  
         [0029]     The shape of the heat conductive block  66  is designed according to the heat flow field distribution inside the heat conductor and the coefficient of thermal conduction obtained in experiment. Here we only use simple texts and associated figures to describe the manufacturing and formation of the disclosed heat conductive block  66 . Please refer to  FIGS. 9, 10A ,  10 B and  10 C.  FIG. 10A  shows the thermal resistance R of the heat dissipating base  70  as a function of the ratio d/D of the cross section width d of the bottom surface of the heat conductive block  66  and the cross section width D of the heat conductive plate  64  in the first embodiment of the invention.  FIG. 10B  shows the thermal resistance R of the heat dissipating base  70  as a function of the ratio h/H of the vertical height h of the heat dissipating base  70  and the vertical height H between the bottom surface  63  of the heat dissipating base  70  and the top of fins  62  in the first embodiment.  FIG. 10C  shows the thermal resistance R of the heat dissipating base  70  as a function of the angle α subtended between the bottom surface  67  and the side surface  68  of the heat conductive block  66  in the first embodiment. Parameters that affect the design of the heat conductive block  66  include the cross section width D of the heat conductive plate  64 , the cross section width d of the bottom surface of the heat conductive block, the vertical height h of the heat dissipating base  70  (the total height of the heat conductive plate  64  and the heat conductive block  66 ), the vertical height H from the lower surface  63  of the heat dissipating base  70  to the top of the fins  62  (the total height of the heat conductive plate  64 , the heat conductive block  66 , and the fins  62 ), the angle α between the bottom surface  67  and the side surface  68  of the heat conductive block  66 , and the thermal resistance R of the heat dissipating base  70 .  
         [0030]     As shown in  FIGS. 10A, 10B , and  10 C, the heat conductive block  66  in the first embodiment has the following features: (1) The cross section width d of its bottom surface is smaller than the cross section width D of the heat conductive plate  64 . The heat dissipating base  70  reaches a minimum thermal resistance, point A in  FIG. 10A , when the ratio d/D approaches 0.5. (2) The vertical height h of the heat dissipating base  70  is smaller than or equal to the vertical height H from the lower surface of the heat dissipating base  70  to the top of the fins  62 ; that is, the height of the heat conductive block is not larger than the height of each fin  62 . When the ratio h/H is between 0.9 and 1.0, the heat dissipating base  70  has a minimum thermal resistance, point B in  FIG. 10B . (3) The angle α between the lower surface  67  and the side surface  68  of the heat conductive block  66  is smaller than 90 degrees. In other words, the area of the lower surface  67  is greater than that of the topmost surface  65 . When a is between 80 degrees and 85 degrees, the heat dissipating base  70  reaches a minimum thermal resistance, point C in  FIG. 10C .  
         [0031]     When the lower surface  67  of the heat conductive plate  64  in the first embodiment is attached to a heat-producing device (not shown), the heat produced by the device can be transferred to each of the fins  62  through the disclosed heat conductive block  66 . The axial-flow fan  12  then provides air convection to bring away the heat.  
         [0032]      FIG. 11  is a side view of the heat sink  80  in a second embodiment of the invention along the  11 - 11  cross section. The biggest difference between this heat sink  80  and the previous one  60  is that the current heat sink  80  contains a heat dissipating base  90  comprised of a heat conductive element  92  and a heat dissipating shell  94  covering over the heat conductive element  92 . The heat dissipating shell  94  and the heat dissipating base  90  are made of different metal materials. For example, the heat conductive element  92  is made of copper and the heat dissipating shell  94  is made of aluminum. The heat dissipating fins  82  are formed together with the heat dissipating shell  94 , and they are only formed on the topmost surface  81  and the side surface  88  of the heat dissipating shell  94 . Otherwise, the heat conductive element  92  is similar to the heat dissipating base  70 . It also has a heat conductive plate  84  and a heat conductive block  86  formed thereon. It should be mentioned that the size, shape, composition, and property of the heat conductive plate  84  and the heat conductive block  86  in the current embodiment are similar to those in the first embodiment. The only difference is that the three-dimensional curved surface of the heat conductive element  92  is covered by the thin piece of heat dissipating shell  94  by soldering or high-pressure mounting. The lower surface  83  of the heat conductive element  92  (i.e. the lower surface  83  of the heat conductive plate  84 ) is also in direct contact with a heat-producing device. In the current embodiment, the parameters in designing the heat conductive block  86  are different from those in the first embodiment only in that the cross section width d is the width of the bottom surface  87  of the heat conductive block  86  plus the widths of the heat dissipating shell  94  on both sides. Therefore, the shape of the heat conductive block  86  is particularly designed according to the heat flow field inside the heat conductor and the coefficient of thermal conduction obtained from experiments. The experimental results in the current embodiment are also similar to  FIGS. 10A, 10B , and  10 C and the heat dissipation effect is the same as in the first embodiment, so we do not repeat here.  
         [0033]     With reference to  FIG. 12 , the composition and structure of the third embodiment of the heat sink  100  are the same as those of the heat sink  80 . The only difference is that: the heat sink  100  has a screw  102  for connecting the heat dissipating shell  94  and the heat conductive block  86 . The heat dissipating shell  94  has a through hole  104 , and the heat conductive block  86  is formed with a trench  106  corresponding to and with the same diameter as the through hole  104 . Another feature of the current embodiment is that when the heat conductive element  92  and the heat dissipating shell  94  are combined together, the screw  102  with a diameter slightly larger than those of the through hole  104  and the trench  106  is inserted into the through hole  104  of the heat dissipating shell  94 . The screw  102  is rotated into the trench  106  on the heat conductive block  86  by hand or machine. The heat dissipating shell  94  is then tightly connected to the heat conductive element  92  through the screw  102 . Therefore, it can avoid increase in thermal resistance due to the connection of two different metals by soldering.  
         [0034]     It should be emphasized here that the side surface of the heat conductive block does not need to be a plane. It can be a smooth and curved surface. The fins can be made into other shapes that have larger heat dissipating areas. These modifications are still within the scope of the invention but not further described herein.  
         [0035]     In comparison with the prior art, a distinct characteristic of the invention is that: all the heat sinks  60 ,  80 ,  100  in the embodiments of the invention have heat dissipating bases  70 ,  90  with a three-dimensional curved surface. They are designed according to the heat flow field inside the heat conductors and data of coefficient of thermal conduction obtained from experiments. Therefore, they solve the problems of inferior heat dissipation in the conventional planar and the cylindrical heat sinks. With the connecting element introduced in the third embodiment, the heat dissipation effect of the disclosed heat sink can be further improved.

Technology Category: 5