The influence of sample processing parameters on the thermal boundary conductance (TBC) between aluminum and aluminum nitride has been investigated by transient thermoreflectance. An evaporated Al layer on the polished substrate yielded a TBC at ambient of roughly 47 MW m(-2) K-1. The largest improvement (by a factor of 5) was obtained by plasma-etching of the substrate and subsequent evaporation of the metal layer. Electron microscopy suggests that the differences in TBC were mainly due to the (partial) elimination of the native oxide layer on the substrate. The importance of an adequate model for data extraction on measured TBC is highlighted. (C) 2011 American Institute of Physics. [doi:10.1063/1.3560469]