Reflection characteristics of displacement deposited sn for LED lead frame

In order to obtain a high reflecting coating for the LED lead frame, Sn displacement deposition was done and the reflection characteristics of displacement deposited Sn was investigated. The Sn coating on the lead frame is expected to result in fine solderability and reduction of the cost relative to Ag coating. Before Sn displacement deposition, Cu electro deposition was carried out to offer a fresh and bright Cu layer (Electroplated Cu, ED Cu) to Sn displacement deposition. With immersion time from 24 min, Sn layer was deposited on ED Cu in the bath of Sn displacement deposition. As a result, optical density of Sn layer was more than 0.8 and the reflectance of that was around 90% at the immersion time 23.5 min, indicating the Sn layer had excellent reflection characteristics compared with Ag. It is also confirmed that lower roughness, smaller grain size and fewer whiskers resulted in higher reflectance of Sn layer, indicating good reflection characteristics for LED lead frame.