Engineered Nanostructures for High Thermal Conductivity Substrates

In the DARPA Thermal Ground Plane (TGP) prograni[1],we are developing a new thermal technology that will enable a monumental thermal technological leap to ail entirely new class of electronics, particularly electronics for use in high-tech military systems. The proposed TGP is a planar, thermal expansion matched heat spreader that is capable of moving heat from multiple chips to a remote thermal sink. DARPA's final goals require the TGP to have ail effective conductivity of 20,000 W/mK, operate at 20g, with minimal fluid loss of less than 0.1%/year and in a large ultra-thin planar package of 10cmx20cm, no thicker than I mill. The proposed TGP is based oil a heat pipe architecture[2], whereby the enhanced transport of heat is made possible by applying nanoenigineered surfaces to the evaporator, wick, and condenser surfaces. Ultra-low thermal resistances are engineered using superhydrophilic and superhydrophobic nanostructures oil the interior surfaces of the TGP envelope. The final TGP design will be easily integrated into existing printed circuit board manufacturing technology. In this paper, we present the transport design, fabrication and packaging techniques, and finally a novel fluorescence imaging technique to visualize the capillary flow in these nanostructured wicks.