Nanostructured thermal interface pastes for microelectronic cooling

Thermal interface materials are needed for improving thermal contacts for the purpose of microelectronic cooling. Through enhancing the conformability by nanostructuring, low-cost and high-performance thermal pastes have been attained, as reviewed in this paper. Particularly effective are pastes that contain thermally conductive components that are in the form of porous agglomerates of nanoparticles, i.e., carbon black and fumed metal oxides. The nanoparticles allow effective filling of the valleys in the surface topography of the mating surfaces. In addition, the porous agglomerate structure allows the solid to be compressible (squishable), thereby facilitating the filling of the valleys. Also effective are nanoplatelets, i.e., graphite nanoplatelets and nanoclay. Nanoclay is exceptionally effective for smooth (0.009 μm) surfaces, due to the small bond line thickness. The optimum solid content tends to be lower when the mating surfaces are smoother and tends to be higher when the thermal conductivity is higher. When the surfaces are smooth (0.009 μm), a low bond line thickness can be even more important than a high thermal conductivity. However, for rough surfaces (15 μm), the thermal conductivity is important. The viscosity does not correlate with the performance. For smooth surfaces, nanoclay paste is recommended. With the overall performance for smooth and rough surfaces considered, carbon black (Tokai) paste is recommended.