Electron spectroscopic investigation (AES/SAM, XPS) of electroplated Ag layers on LED-CuSn-lead frames: Combined phenomena of segregation and corrosion

Summary

In order to improve LED fabrication processes inclusive handling in LED packaging and final tinning details of two interlinked phenomena were studied by the use of AES/SAM and XPS: Cu segregation during low-temperature thermal stress as well as different stages of (Cl, S) corrosion which take place at the surface of Ag thin films electroplated on lead frames consisting of CuSn material. In the case of the Ag corrosion a probable mechanism was observed, namely that the initial step is connected with an enlarged presence of Cl in the topmost corrosion layer. In subsequent steps this chlorinated Ag thin film was substituted by sulphatic, afterwards sulphidic silver at the surface. In Ag material adjacent to the Cu segregates all corrosive processes proceed in an especial intense manner, which is demonstrated by the fact, that the Cu-“necks” induced by the segregation process quickly and intensively include deeper located Ag regions into the corrosion process.