Abstract: Cu-Sn IMC solder joints for chip stack interconnects were prepared via transient liquid phase bonding and subsequently subjected to isothermal aging at 150 ℃. The microstructure evolution and mechanical properties of Cu-Sn IMC solder joints modified with Al nanoparticles were studied under aging conditions. The results show that the rapid growth of interfacial layer and the formation of voids in Cu-Sn IMC solder joints can be effectively inhibited by adding trace amounts of Al nanoparticles. During isothermal aging, the Cu₃Sn interfacial layer in both Cu-Sn-Cu and Cu-Sn0.3Al-Cu IMC solder joints gradually thickened, but the growth rate of Cu₃Sn layer in Cu-Sn0.3Al-Cu IMC solder joints was always lower than that in Cu-Sn-Cu solder joints, and the voids were significantly less than that in Cu-Sn-Cu solder joints. After 300 h of aging, the shear strengths of the two IMC solder joints were 23.1 and 26.5 MPa, respectively. When the aging time was extended to 1 500 h, the shear strengths of the two IMC solder joints decreased to 13.4 and 17.6 MPa, representing reductions 44.2% and 35.3%, respectively. At the initial aging stage, the fracture morphology of Cu-Sn-Cu and Cu-Sn0.3Al-Cu IMC solder joints exhibited transgranular fracture. As aging progressed, the fracture morphology of Cu-Sn-Cu IMC solder joints gradually transitioned to an intergranular fracture, whereas Cu-Sn0.3Al-Cu IMC solder joints retained its transgranular characteristics.