Abstract: Quasi-in-situ method was carried out to study the effects of β-Sn grain orientation and grain boundary feature on the growth behavior of interfacial intermetallic compounds (IMCs) in Cu/Sn3.0Ag0.5Cu/Cu(Cu/SAC305/Cu) micro solder joints under different aging temperatures. The results showed that the IMCs containing Cu₆Sn₅ + Cu₃Sn phases at both interfaces of the micro solder joints grew symmetrically under all the aging conditions, proving that β-Sn grain orientation and grain boundary played no obvious effect on the interfacial IMCs growth either between the two interfaces of a same joint or those from different joints. While with increasing aging temperature, the morphology and thickness of the interfacial IMCs were changing apparently. Scallop-type Cu₆Sn₅ and thin discontinuous Cu₃Sn formed at the interfaces after aging at 100 ℃; scallop-type Cu₆Sn₅ and thin continuous Cu₃Sn formed at the interfaces after aging at 125 ℃ and bilayer structured IMCs containing Cu₆Sn₅ and Cu₃Sn formed at the interfaces after aging at 150 ℃. The increasing aging temperature accelerated the diffusion of Cu and Sn atoms, which could promote the transition of Cu₆Sn₅ from scallop to layer and the rapid growth of Cu₃Sn. Finally, based on the variation of interfacial IMCs thickness with aging time, the growth curves of the interfacial IMCs layers under different aging conditions were obtained which may be helpful for reliability assessment of Sn-based micro solder joints.