Sintering of mixed Cu[sbnd]Ag nanoparticles pretreated by formic acid vapor for Cu[sbnd]Cu low temperature bonding

Abstract

In this work, a CuCu low temperature bonding method by using mixed CuAg nanoparticles (NPs) paste was proposed. To remove the oxide on the surface of Cu NPs, formic acid vapor pretreatment process was applied to treat the mixed CuAg NPs paste at 180 °C for 30 min. After the 30-min pretreatment, the oxide on Cu NPs was effectively reduced and the bonding quality has significantly improved. A reliable CuCu bonding was successfully achieved at the temperature of 250 °C for 30 min under a low pressure of 5 MPa after the pretreatment of formic acid vapor and the average shear strength achieved approximately 60.5 MPa. For mixed CuAg NPs paste sintering at 250 °C, the average resistivity reached 39.7 μΩ·cm after the pretreatment. Besides, with the bonding temperature increasing, especially after the pretreatments of formic acid vapor, the bonding interfaces became more compact and the fracture surfaces exhibited more distinct ductile deformations, which further illustrates the high quality of bonding. According to the results, this bonding technology is promising to be widely used in power device packaging.