Nowadays, many applications require low soldering temperature process to avoid chip warpage during soldering. Two low melting temperature alloys, In-48Sn and Sn-58Bi, are receiving the most attentions. Sn-58Bi, with superior fatigue resistance and tensile strength, has been widely used in the industry. However, the brittle property of Bi-containing phases restricts the application of this materials. In-48Sn, with excellent mechanical properties and thermal conductivity, has not been fully investigated yet. Therefore, this study focused on the interfacial reactions between Cu and liquid/solid In-48Sn solder, especially the appearance of the Cu2In3Sn phase at low temperature. In order to obtain an artifact-free microstructure that is not damaged by mechanical polishing, cryogenic broad Ar beam ion polishing was applied. Electron probe micro-analyzer and X-Ray diffractometer were also used to identify the composition and phase structure at the interface.