The wetting as a multi scale phenomenon, including micro- and nano-scale aspects, is considered to be the essential step in the evaluation of the transport phenomena during metal/ceramics joining with active filer metal. Micro-scale aspect deals with diffusivity at the interface and into the bulk, as well as mass transfer around the grain boundary grooves (GBG) of the ceramic surface. In that sense, the explanation of mass transport mechanism around the GBG’s is presented. Mathematical analysis is based on experimental values taken from literature. Nanoscale wetting aspect is an atomistic approach, which includes the investigation of phase boundary structure. The mathematical model, which enables the contact angle calculation depending on the features of crystal lattice and interactions between atoms and molecules of the liquid and solid phases, is proposed.