Song-Zhu Kure-Chu

Multilayered Sn/Ag 3 Sn electroplating on Cu alloys for high reliable electronic/electric materials

We report a multilayered Sn/Ag 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.

Sliding friction, wear and tribofilm formation of silver films electro-plated on copper alloy sheets

This study is aimed at clarifying the mechanism of wear process for Ag plating through a one-way sliding wear test. The samples of different hardness Ag plating on copper alloys were prepared as coupon and embossment specimens, which simulated terminal contacts. During the sliding test, the contact resistance and the friction coefficient are measured. The surface and cross-section morphologies, roughness, tribo-film formation, and wear volume of the Ag films after wear tests were investigated and the wear mechanism was discussed. As results, the hard Ag plating film (120 Hv) exhibited higher contact resistance comparing to the soft Ag plating film (80 Hv). The soft Ag film delivered a larger wear scar on embossment and wider wear trace on coupon specimens compared to the hard one. The overall wear volume of hard Ag film was less than that of soft Ag film, which can be attributed to the fine crystalline structure of hard Ag. Moreover, the observation of tribofilms formed on the Ag films after wear tests suggested that a mixed-type of adhesive and abrasive wears occurred for both of soft and hard Ag films.