ELECTROCHEMICAL MIGRATION FAILURE OF PURE TIN UNDER BROMIDE-POLLUTED THIN ELECTROLYTE LAYER

Abstract

The electrochemical migration (ECM) time to failure (TTF) tests for pure tin in the bromide-containing environment were carried out using the thin electrolyte layer (TEL) method. In-situ electrochemical measurement was made to monitor the ECM behavior while the changes of surface morphology and localized pH during the ECM process were real-time observed using the 3D optical digital microscope. Microstructure and composition of products obtained after the ECM tests were characterized using the scanning electron microscope, energy-dispersive spectrometer and X-ray diffractometer. Results indicated that the growth rate of dendrite increased with bromide ion concentration at low bromide concentration levels, and it decreased at medium concentration levels. Tree-like tin dendrites covered with white precipitates are formed after the ECM tests. As for the high bromide ion concentration condition, no dendrite can be found and a thick layer of precipitate is formed between the twin electrodes. This precipitate layer has a higher thickness than the electrolyte layer, which can act as a barrier layer retarding ionic migration and thus inhibiting the ECM failure. Relevant mechanism has been proposed to clarify the effect of bromide ions on the ECM of pure tin under the thin electrolyte layer.