Thermal cycle reliability of Cu-nanoparticle joint

Abstract

The improvement of the performance of power electronic devices requires the development of new Pb-free joint materials that are capable of enduring high temperatures more than 200°C. Cu-nanoparticle joints are considered to be promising for this purpose owing to their low cost, high melting point, and good thermal conductivity. There have, however, been few studies on the thermal cycle reliability of such joints. In the present study, thermal cycle tests involving up to 1000 cycles of −40/150°C and −40/200°C, respectively, were conducted on Cu-nanoparticle and soldered Sn–0.7wt.%Cu joints between an Al2O3 chip and Cu–65wt.%Mo plate. The Cu-nanoparticle joint was found to be undamaged by the −40/150°C thermal cycles at a joint temperature of 300°C, but completely broken at the joint interface by the −40/200°C thermal cycles. The Cu-nanoparticle joint interface was subsequently strengthened by increasing the joint temperature to 350°C, and this enabled endurance of the −40/200°C thermal cycles. However, the soldered joint was completely broken by −40/200°C thermal cycles owing to the melting point of Sn–0.7wt.%Cu (227°C) being much lower than that of Cu (1085°C). The Cu-nanoparticle joint thus exhibited superior thermal reliability compared to the soldered joint.