1.  Field of the Invention
This invention generally relates to a heat transfer device and manufacturing method thereof, and more particularly to a heat transfer device and manufacturing method thereof to simplify the manufacturing process, reduce costs, and enhance heat conductivity. 
2.  Description of Related Art
To fast dissipate the heat generated from operation of the electronic devices, conventionally a radiator will be disposed on the heating element of the electronic device provide a larger area for heat dissipation.  Further, a cooling fan will be used to provide a cool air current to further dissipate the heat.  Hence, the electronic device can keep within the range of the operational temperature.  For example, the radiator and the cooling fan are used in the CPU, North Bridge, and graphic chip of the personal computer, which can generate high heat. 
It should be noted that recently a heat transfer device is developed by using transformation between liquid state and gaseous state.  This heat transfer device has the advantages of high conductance (30-6000 W), long distance (0.3-10 m) and single directional transferability, and flexibility, and is not affected by the gravity.  Hence, it gradually replaces the conventional radiator. 
FIG.  1 is a conventional heat transfer device.  Referring to FIG.  1, the conventional heat transfer device 100 comprises a evaporator 110, a loop heat pipe 120, and a condenser 130.  The evaporator 110 comprises a metal tube 112 and a porous core 114.  The porous core 114 is disposed inside the metal tube 112.  The evaporator 110 is disposed on the heating device such as CPU.  The loop heat pipe 120 is connected to the evaporator 110 and has a proper amount of working fluid therein.  The condenser 130 is disposed on the loop heat pipe 120 to condense the steam in the loop heat pipe to the liquid state. 
When the heating device generates high heat, the evaporator 110 will receives the heat and thus the working fluid in the porous core 114 will be heated up and enter into the loop heat pipe 120 and the condenser 130.  The condenser 130 then condenses the steam in the loop heat pipe to the liquid state.  The capillarity attraction of the porous core 114 will attract the working fluid in the loop heat pipe 120 back to the evaporator 110 and the porous core 114 therein.  Hence, this design form a loop so that the working fluid can flow circularly in the loop heat pipe 120 and transfer the heat generated by the heating device to the condenser 130. 
FIGS.  2A-2C show the manufacturing process of the conventional heat transfer device.  Referring to the FIGS.  2A-2C, the manufacturing method of the conventional heat transfer device 100 directly fuses a porous core 114 inside a hollow metal tube 112 (as shown in FIG.  2A).  Then the two caps 140 are welded at the two ends of the hollow metal tube 112 (as shown in FIG.  2B).  Then the loop heat pipe 120 is welded on the caps 140.  A heat conducting platform 150 is welded at the bottom if the hollow metal tube 112 so that the high heat of the heating device 10 can be transferred from the heat conducting platform 150 to the evaporator 110 (as shown in FIG.  2C).  It should be noted that the manufacturing method of the conventional heat transfer device has the following disadvantages:
1.  The porous core is directly fused inside the hollow metal tube, which is costly and very difficult to implement and to control the quality. 
2.  Two caps, the loop heat pipe, and the heat conducting platform are fixed by welding, which is difficult to implement because there several welding points.  Further, the porous core is easy to be damaged during the welding process. 
3.  The heat conducting platform can only conduct the heat to the lower part of the evaporator.  Hence the heat conductance is too low. 
Further, there is another manufacturing method for the conventional heat transfer device.  This method is very similar to the first conventional method.  The difference is that the porous core is fused by using the module and is embedded into the hollow metal tube by thermal connecting technology.  However, this method also has the above disadvantages.  Further, because the end of the porous core providing the working fluid is difficult to be tightly connected to the hollow metal tube by thermal connecting technology, the working fluid is easy to leak.