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 fig7 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 . 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 . 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 fig9 a , 10 b and 10 c . fig1 a 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 . fig1 b 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 . fig1 c 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 . as shown in fig1 a , 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 fig1 a , 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 fig1 b . ( 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 fig1 c . 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 . fig1 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 fig1 a , 10b , and 10 c and the heat dissipation effect is the same as in the first embodiment , so we do not repeat here . with reference to fig1 , 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 . 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 . 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 .