A substrate metallization for soldering, with a Pb-free solder or a eutectic SnPb solder (4), to a thin film under-bump-metallization (UBM) of a Si die, comprising: a substrate (1), a layer of Cu (20) formed on a portion of the substrate (1), a layer of Ni (21) formed on the Cu layer (20), an oxidation protection layer (22), and a Ni-barrier layer (23), between the Ni layer (21)and the oxidation protection layer (22), adapted to inhibit diffusion of Ni from the Ni layer (21) to the solder (4) during a reflow process or during high temperature storage.