A scanning transmission electron microscopy and an energy dispersive X-ray analysis of one non-annealed and one annealed sample (423 K for 4 hours) was performed. The results showed small and large voids appearing within the non-annealed and annealed samples respectively. In addition, chlorine segregated from the bulk into the voids. Ab initio calculations determined the formation energies for dilute solutions of chlorine and vacancies in Cu, Cu3Sn and Cu6Sn5. Results suggest that dilute solutions energetically favor vacancies, indicating a low chlorine solubility and a driving force for segregation.