Reflection characteristics of electroless deposited Sn-3.5Ag for LED lead frames

The characteristics and reflection properties of a Sn-3.5 wt.%Ag (hereafter, Sn-3.5Ag) thin film on a light emitting diode (LED) lead frame were investigated in this study. The advantages of a Sn-3.5Ag layer, namely its good solderability and low cost compared to Ag, are attractive for LED applications. A Sn-3.5Ag layer was deposited in an electroless process on an electro-plated copper substrate with bath immersion times of 2 to 10 min. At an immersion time of 4 min, the optical density and reflectivity of the Sn-3.5Ag deposits was 1.91 D and approximately 98%, respectively. The reflectivity of the Sn-3.5Ag deposition layer decreased with increasing surface roughness and with larger grain size. The reflectivity of a sample aged for 100 days decreased approximately 3.6% compared to the as-plated Sn-3.5Ag sample.