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 investig ated 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 t o contamination from elements such as sulphur and chlorine found on th e silver surface after thermal treatment, while Ti/Ni metal is sensiti ve to oxidation. NiO, Ni(OH)2, NiOOH and Ni2O3 species were found on t he Ni as deposited surface. The surface compositions were correlated t o 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.