**6. Conclusion**

In this chapter, several surface modification methods for improving the thermal performance of a two-phase heat spreader are introduced and discussed. Forming a wettability pattern on a surface enhances the evaporation of a droplet by elongating the length of the contact line. Thus, integrating the wettability pattern to the evaporator of a two-phase heat spreader is probably to enhance the thermal performance of the heat spreader, which is proved by the temperature uniformity enhancement of an ultrathin vapor chamber utilizing an evaporator with a wettability patterned surface. Changing the wettability of the condenser to superhydrophobic can also enhance the thermal performance by modifying the condensation mode from filmwise condensation to dropwise condensation which shows at least 3 times the heat transfer rate of the previous mode. Nanostructuring the microstructure to form a multiscale micro/nanostructured wick structure is also an efficient way to enhance the thermal performance of a two-phase heat spreader. It not only enhances the heat transfer rate on the evaporator but also increases the backflow ability of the wick structure, greatly improving the overall thermal performance of a two-phase heat spreader.
