The influence of current on the structure of the intermetallic compound in solder alloys

This paper investigates the impact of applied current on the structure of Cu₆Sn₅ and Cu₃Sn intermetallic layers and compounds within the volume of the SAC305 solder alloy. The study focuses on the transition region between a copper electrode and the solder alloy. Direct current at magnitudes of 25 A and 30 A was applied for durations of 30 and 90 minutes, alongside samples fabricated without current application. After the samples were prepared, the surfaces were refined through sanding and subsequent polishing with diamond pastes. To enhance the quality of data obtained from these samples, the surfaces were etched, improving the visibility of their microstructure. Statistical analysis of the intermetallic layer thickness at the Cu electrode–solder alloy interface was conducted. The results revealed a significant influence of applied current on the width of the intermetallic layers. Measurements demonstrated a polarity-dependent effect on the layer thickness, that samples formed under current exhibiting substantially thicker layers at the positive electrode compared to the negative electrode. Additionally, the samples with applied current showed a significant increase in the size of intermetallic compounds within the solder alloy, reaching dimensions of several millimeters. The final part of the research involved elemental analysis to confirm the composition of the intermetallic compounds. This analysis validated the presence of Cu6Sn5 and Cu3Sn.