Abstract The surface compositions of three different back‐side metals: Ti/Ni/Au 0.1/0.4/0.1 μm, Ti/Ni/Ag 0.1/0.4/0.1 and 0.1/0.4/2 μm and Ti/Ni 0.1/04 μm after thermal treatment at 180°C in air were investigated by means of XPS technique. In the Ti/Ni/Au metal the Ni diffusion through the Au layer was observed, while in the Ti/Ni/Ag metal Ni was not found on the silver surface. Ti/Ni/Ag was found to be sensitive to contamination from elements such as sulphur and chlorine found on the silver surface after thermal treatment, while Ti/Ni metal is sensitive to oxidation. NiO, Ni(OH) 2 , NiOOH and Ni 2 O 3 species were found on the Ni as deposited surface. The surface compositions were correlated to their wetting property using the Pb88Sn10Ag2 and Pb95.5Sn2Ag2.5 wt.% soft solder alloys. The wetting was studied measuring the contact angle between the surface and the drop of molten solders.