Low Temperature Solid State Bonding of Cu-In Fine-Pitch Interconnects

Cu-In fine pitch interconnects are a viable approach for low temperature bonding technologies in 2.5 D and 3D integration. The unique metallurgical phenomena regarding the phase formation and growth of intermetallic compounds (IMCs) in the Cu-In system affect both processing conditions and the resulting interconnection properties. In this work, we investigate the formation Cu-In joints below 150 °C, i.e. in the solid state, under ambient conditions. Dies with Cu interconnects and In caps (25 μm diameter, 55 μm pitch) were bonded in a flip-chip process at moderate pressures and subsequently investigated by means of mechanical testing, cross-sectioning and microstructural analysis. In particular, we reveal the presence of stable interconnects exhibiting a ductile bonding zone. The resulting die shear strengths are in the range of 15-20 MPa.