CHARACTERIZATION AND RELIABILITY OF TI/NI/AU, TI/NI/AG AND TI/NI BACK-SIDE METALLIZATIONS IN THE DIE-BONDING OF POWER ELECTRONIC DEVICES

The surface compositions of three different back-side metals: Ti/Ni/Au 0.1/0.4/0.1 mum, Ti/Ni/Ag 0.1/0.4/0.1 and 0.1/0.4/2 mum and Ti/Ni 0.1/0.4 mum after thermal treatment at 180-degrees-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 Ni2O3 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.