Microstructural and micromechanical characterization of sintered nano-copper bump for flip-chip heterogeneous integration

Copper nanoparticles (CuNPs) sintering for flip-chip interconnects is a promising solution for 3D and heterogeneous integration to overcome the limitation of solder materials. To this end, we perform the photolithographic stencil printing method to pattern CuNPs, and the form of flip-chip interconnects is completed after CuNPs sintering process. This paper aims to study the effect of sintering processing parameters (time, pressure, temperature) on the mechanical properties of CuNPs bumps when applying the novel method to approach the Cu interconnects. We fabricated seven groups of specimens of sintered CuNPs bumps, built with a diameter of 100 μm and sintered. The nanoindentation tests assessed the mechanical property to get Young's modulus and hardness. Results clarify that Young's modulus is strongly affected by pressure. An suggested combination of parameters (the 25 MPa and 260 °C for 15 min) give the highest modulus of 126 GPa and the hardness of 1.76 GPa. Moreover, the observations by scanning electron microscopy (SEM) reveal the microstructure and porosity evolution versus different processing parameters.