Electrolytic Cu plating and anti-tarnish influence on Cu Layer oxidation

In Semiconductor package assembly process, Cu lead frame (LF) must be exposed to high temperatures in die bond, wire bond heat plates before encapsulated, and easy to be oxidized [1], [2], [3], N2 and H2 forming gas is applied to prevent LF surface from oxidation. But we still encountered serious "Cu accumulation" on die bond heat block. Cu accumulation was caused by LF Cu surface oxidation. In this paper Cu oxidation prevention factors were studied together with lead frame suppliers, key factors such as electrolytic copper plating parameters, anti-tarnish types were investigated and optimized.Cu oxidations were thoroughly studied in two aspects. One is anti-tarnish layer protection effect, different anti-tarnish types were compared by actual Cu accumulation performance and follow with dipping process optimization, which was characterized by Cu surface contact angle, X-ray Photoelectron Spectroscopy (XPS).2nd factor is electrolytic Cu layer structure influence on Cu Oxidation, Scanning Electron Microscopy (SEM), Focused Ion Beam (FIB) was used for surface morphology and Cu layer internal structure investigation. Result indicates different Cu layer structure have different oxidation performance. Further in-depth study indicates that different plating chemical solution setup influence Cu layer grain structure, which is the root cause.With this study, key Cu layer oxidation influence factors were identified and optimized, Cu accumulation issue solved.