Experimental Characterization of Cascaded Vapor Chambers for Spreading of Non-Uniform Heat Loads

Thermal management of heterogeneous electronic devices relies on spreading high local heat fluxes in the package lid. The use of intra-lid vapor chambers is an attractive approach if they can be designed for the thermal management of a large total heat load simultaneous with localized high-flux hotspots. Conventional vapor chambers, having a single vapor core, require thick evaporator wicks to avoid the capillary limit at high total power, but these thick evaporator wicks impose a large conduction resistance to hotspots. The recently proposed cascaded multi-core vapor chamber (CMVC) concept consists of a bottom-tier comprising multiple vapor cores that can each diffuse high heat flux hotspots before they reach the top tier, which acts as a conventional single-core vapor chamber. The current study experimentally investigates the use of cascaded vapor chambers for heat spreading of a non-uniform heat load to illustrate this design rationale. The thermal resistance of a solid copper benchmark, a conventional vapor chamber, and a cascade of two vapor chambers are compared for non-uniform heat input. Experiments are performed by interfacing the heat spreaders with a central heater generating the peak heat flux surrounded by a film heater that produces a lower heat flux background power; the other side of the spreaders is interfaced to a cold plate to provide a controlled boundary condition. The results demonstrate that the cascaded vapor chambers offer a notable reduction in thermal resistance relative to the conventional vapor chamber. The enhancement in performance is attributed to the local dampening of the peak heat fluxes at a low thermal resistance, thereby reducing the total thermal resistance of the cascaded vapor chambers relative to the standalone vapor chamber. This result reveals that cascades of vapor chambers have the potential to perform better than conventional vapor chambers through attenuation of hotspots at a low thermal resistance.