Reflectivity and Thermal Shock Properties of Sn-3.5Ag Electroless-plated Deposit for LED Lead Frames

The surface roughness and reflection characteristics of electroless-plated Sn-3.5 wt%Ag on a LED (light emitting diode) lead frame were investigated. Cu electroplating was carried out prior to electroless plating of Sn-3.5Ag to improve the reflectivity of the Sn-3.5Ag deposit. A thermal shock test was performed to evaluate the stability of the deposits, namely the surface roughness and the reflectivity of the Sn-3.5Ag layer. The experimental results revealed that the surface roughness of the Sn-3.5Ag deposit was 0.135 mu m (arithmetical verage roughness, R-a), 1.77 mu m (maximum height roughness, R-max) and the reflectivity was 1.86 GAM. After 500 thermal shock cycles of the Sn-3.5Ag deposit between 85 degrees C and -55 degrees C, the surface roughness became 0.145 mu m (R-a) and 1.93 mu m (R-max), and the, reflectivity was 1.76 GAM, which indicates that the Sn-3.5Ag deposit was stabilized by 500 thermal cycles.