Large area pressureless Cu-Cu bonding using formic acid-treated Cu particles for power device packaging

When large-area die-attach bonding, high pressure needs to be applied to ensure sufficient bonding strength. In order to solve this problem, this work provides a pressureless sintering method. The copper substrate and copper nanoparticles are modified by formic acid. The surface is coated with copper formate layer, which can protect the internal copper core from oxidation and can be decomposed into new active nano copper particles at low temperature, to realize pressureless sintering. The shear strength can reach 10MPa after annealing at 300 ℃ for 30min, and the influence of substrate ' s roughness on the shear strength is studied. According to our experiments, the joints aged in ambient atmosphere exhibited much higher strength compared with the ones that aged in vacuum. Our work provides a cost-effective way for die-attach bonding.