Enhancing mechanical properties via the dual effect of Ni addition and temperature gradient for 5 μm Cu/Sn-3.0Ag-0.5Cu/Cu transient liquid phase bonding

Abstract

More recently, transient liquid phase bonding was widely considered to be a potential bonding method in 3D-IC technology as the full intermetallic compounds (IMCs) joints were characterized by superior bonding strength and reliable high temperature service. Nevertheless, preferred grain orientation and coarsening grains have been the shortcoming for traditional Cu/Sn/Cu transient liquid-phase bumps in heterogeneous integration. To alleviate such issues, Ni/Sn/Cu system was adopted to improve mechanical properties. Moreover, the thickness of joints was reduced to 5 μm for staying ahead of the trends of the miniaturization of electronic products. In this research, the microstructure of Cu/Sn-3.0Ag-0.5Cu/Cu, Cu/Sn-3.0Ag-0.5Cu/Ni, and Ni/Sn-3.0Ag-0.5Cu/Cu micro-bumps after transient liquid-phase bonding was investigated. With dissolution of Ni from substrate, the intermetallic compounds have diverse texture and refined grain. The distinct correlation between intermetallic compounds structure and Ni content was investigated on Ni substrate being in hot end or cold end. After shear testing, as compared to Cu/Sn-3.0Ag-0.5Cu/Cu, Ni/Sn-3.0Ag-0.5Cu/Cu showed extremely outstanding strength via replacing Cu substrate by Ni substrate. As compared to conventional Cu/solder/Cu full intermetallic structure, the shear strength increased 103.28% as Ni at the cold end. In this study, microstructure, grain analysis, and the fracture path observation after shear test were carried out to clarify the strengthening mechanisms of Ni.