In situ formation of Cu-Sn-Ni intermetallic nanolayer as a diffusion barrier in preplated lead frames

A technique for impeding Cu outdiffusion in Cu alloy based preplated lead frames has been developed by electroplating a 3-4 nm thick Sn layer on a Cu alloy base prior to electroplating a Ni layer. A 10-14 nm thick epitaxylike and dense (Cu,Ni)₃Sn intermetallic-compound (IMC) layer is automatically formed en route of diffuse reaction, which leads to a drastic reduction in Cu outdiffusion and hence improves significantly the protection of the lead frames against oxidation and corrosion attack. The estimated Cu diffusion coefficient in the IMC interlayer is about 1.6 × 10^-22 m²/s at 250°C.