Thermal performance of vapor chambers under hot spot heating conditions

Use of heat pipes (or vapor chambers) is considered as one of the promising technology to extend the capability of air cooling. This paper reports the test results of vapor chambers using two different sets of test heaters (copper post heater and silicon die heater). Experiments were conducted to understand the effects of non-uniform heating conditions on the thermal performance of vapor chambers. In contrast to the copper post heater which provides ideal heating condition, silicon chip package was developed to replicate more realistic heat source boundary conditions of microprocessors. The chip contains three metallic heaters: a 10 x 12 mm heater in order to provide uniform heating, a 10 x 3 mm heater in order to simulate a localized heating, and a 400 x 400 mu m heater in order to simulate the hot spots on actual microprocessors. In the experiment, the highest heat flux from the hotspot heater was approximately 690 W/cm(2). Test results indicated that both conduction heat transfer and phase-change phenomena played key roles in the evaporator. The study found that the evaporator resistance was almost insensitive to non-uniform heating conditions, but was clearly dependent on the amount of power applied over the die area. In addition, a simple one-dimensional thermal model was developed to predict the performance of vapor chambers for non-uniform heating conditions and the results were compared against experiments.