A highly reliable die bonding approach for high power devices by low temperature pressureless sintering using a novel Cu nanoparticle paste

A novel Cu nanoparticle (NP) paste with the capability of pressureless sintering at low temperature in nitrogen is developed using a type of easily synthesized Cu NPs. The feature of bimodal size distribution of Cu NPs can be inherited to the Cu NP paste, which facilitates the formation of dense as-sintered microstructure, mainly consisted of Cu bulks, in sintered joints. The optimization of the sintering process condition has been achieved by using Taguchi method, and so-obtained Cu paste joints show shear strength as high as 65.24 MPa. Moreover, the formulation of the solvent containing ethylene glycol (EG) and glycerol with an optimized weight ratio, which is employed for preparation of the Cu NP paste, has also been demonstrated to be crucial for the formation of Cu bulks in joints and so-induced superior bonding strength. Finally, the results of high temperature storage (HTS) tests of Cu paste joints after aging at 200 degrees C for 600 h show that there is a slight degradation of bonding strength of joints, mainly due to the generation of voids at the Cu-paste/Cu interface.