Sintering of mixed Cu-Ag nanoparticles pretreated by formic acid vapor for Cu-Cu low temperature bonding

In this work, a Cu-Cu low temperature bonding method by using mixed Cu-Ag 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 Cu-Ag NPs paste at 180 degrees 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 Cu-Cu bonding was successfully achieved at the temperature of 250 degrees 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 Cu-Ag NPs paste sintering at 250 degrees C, the average resistivity reached 39.7 mu omega.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.

Automated summary

This work proposed a Cu-Cu low temperature bonding method using mixed Cu-Ag nanoparticles paste. The oxide on the surface of Cu nanoparticles was effectively reduced and the bonding quality significantly improved after the pretreatment with formic acid vapor. Reliable Cu-Cu bonding was achieved at 250 degrees C with a low pressure of 5 MPa after formic acid vapor pretreatment, and the average shear strength reached approximately 60.5 MPa. The average resistivity of the mixed Cu-Ag nanoparticles paste after pretreatment at 250 degrees C was 39.7 mu omega.cm. The bonding interfaces became more compact and showed distinct ductile deformations with increasing bonding temperature, indicating high quality bonding.