Thermal and compositional fields to maneuver Cu 6 Sn 5 intermetallic growth on (111) nanotwinned copper substrate

The microstructure of the Cu 6 Sn 5 phase plays a pivotal role in the functionality of microbumps utilized in 3D packaging. In this study, we present an experimental methodology aimed at maneuvering the orientation and morphology of Cu 6 Sn 5 grains formed on (111) nanotwinned Cu substrate, achieved through variations in reflow temperatures (260 degrees C and 300 degrees C) and initial Cu proportion in solder (ranging from 0 to 3.0 wt%). At 300 degrees C and lower initial Cu concentrations (0 and 0.7 wt%), irregularly arranged roof-type Cu 6 Sn 5 grains exhibiting a pronounced {2110 } texture were observed. Conversely, typical scallop-type Cu 6 Sn 5 grains displaying a specific preferential {2113 } texture were identified at this temperature for Cu concentrations of 1.5 and 3.0 wt% At 260 degrees C, the scallop-type morphology was solely present at all Cu composition variants. The differing rates of solute controlled intermetallic phase clustering mechanism at altered solubility limits and magnitudes of thermodynamic driving force for different temperatures, can decide the relative loss of interface coherency and subsequently change the preferred orientation direction of evolving interfacial structures. Our findings demonstrate that the precise control over soldering temperature, solder Cu composition, and the microstructure of Cu UBM can enable the attainment of Cu 6 Sn 5 microstructure with a designated orientation and morphology.