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as the power dissipated by the devices increases, and the devices get smaller, the heat densities increase rapidly, and heat dissipation gets more localized. the heat fluxes approach 100 w/cm2 and local heat fluxes at hot spots are even higher, however the proper junction temperature must be maintained to meet performance and reliability requirements. in some cases this temperature has to be as low as 85 degree c or even lower. this trend drives the need for the fast heat spreading. one such device is a vapor chamber.

wei et al. [1] attempted to evaluate the feasibility of integrating vapor chambers into a device package as a heat spreader or lid to enhance the heat spreading and to reduce the conduction resistance. in addition, they attempted to quantify the thermal benefit of vapor chamber heat spreader as compared to a solid metal heat spreader. a vapor chamber, just as a heat pipe, is a heat spreading device with large effective thermal conductivity due to the phase change phenomenon.

a typical vapor chamber consists of two thin layers of sintered copper powder with a vacuum space in the middle enclosed by two thin stamped copper parts. there is also a small amount of liquid, typically water, saturated in the wick. unlike the heat pipe, the vapor chamber consists of only two sections, an evaporator and a condenser, and the condenser covers the entire top surface of the evaporator. heat enters the evaporator section located on top of the heat source.

the liquid saturated in the wick evaporates, and the vapor carries the heat into the vapor space. the vapor flows from the higher pressure region in the evaporator to the condenser section and rejects the heat to the ambient air through condensation and external cooling. the liquid flows back to the evaporator section through the capillary action in the wick structure.

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