Reactive spreading and dewetting of liquid SnPb solder on Cu thin films

The SnPb solder ball was reflowed on the Cu film in a flow of reducing gas, and the reactive spreading process was in situ recorded by a CCD camera. On the thicker Cu films, it was observed that dewetting did not happen even if the Cu₆Sn₅ intermetallic compounds spalled into the liquid solder. However, on the thinner Cu films, dewetting would occur when the liquid SnPb solder consumed the underneath Cu film. It was concluded that the thickness of Cu film played an important role in determing the dewetting behavior. We set up a simplified model to explain this phenomenon, which was also supported by experiments.