Cu-Cu joint formation by low-temperature sintering of self-reducible Cu nanoparticle paste under ambient condition

• A novel self-reducible Cu nanoparticle paste was proposed. • A high Cu-Cu bonding strength of over 50 MPa can be achieved at 250 °C under air condition. • The sintering mechanism was studied. The development of WBG (wide bandgap) semiconductors has put forward higher requirements for packaging and interconnection technology. Cu sintering is widely considered as an advanced interconnection technology which can be used in high temperature and high power density service. In this paper, a new type of self-reducible Cu nanoparticle paste was proposed to solve the problems of easy oxidation and high sintering temperature of normal Cu nanoparticles. The proposed Cu paste was developed by mixing formic acid treated Cu nanoparticles, reducing solvents and MOD (metal organic decomposition) solutions. Based on the new type of self-reducible Cu nanoparticle paste, Cu-Cu bonding experiments were carried out with different bonding temperature and time, and a reliable Cu-Cu joint with a high shear strength of 52.01 MPa can be achieved at 250 °C under ambient condition, without any assistance of reducing or inert atmosphere. In addition, the MOD assisted self-reduction and sintering mechanism was proposed after shear strength testing, element composition analyzing, cross-sectional morphology and fracture structure observation, which can provide an effective theoretical support for the practical application of Cu-Cu bonding.