2014 Volume 7 Issue 1 Pages 79-86
We report a multilayered Sn/Ag3Sn film electroplated on Cu alloys with high reliability as promising coating materials for LED lead-frames and for electric connectors. The multilayered Sn/Ag films consisted of an Ag-Sn alloy film with 30-80 nm-thick as Ag3Sn phase covered on a 1 μm-thick Sn film on Cu alloy substrates. The as-deposited Sn/Ag3Sn films exhibited a high specular reflectivity around 70% at the wavelengths of 480 nm, which was lower than a commercial bright Ag film with total reflectivity of 90% but much higher than a commercial bright Au film in 24% at the same wavelength. It was found through an accelerated sulfuring test that, the reflectivity of the Sn/Ag3Sn films was almost unchanged even after immersing in a 0.2% (NH4)2Sx solution for 60 min, compared to the abrupt decrease to 15% for the conventional Ag film even after immersing for 10 min. The excellent sulfuring resistance and durability of the multilayered Sn/Ag3Sn films can be attributed to the existence of a stable SnO2 film existed on the surface of Ag3Sn alloy, which was revealed by a UPS analysis in a vacuum chamber by heating at 473-673 K, thus protecting underneath Ag3Sn alloy film and inhibiting the chemical reaction of Ag and S2− ions.