Thermal and Compositional Fields to Maneuver Cu6Sn5 Intermetallic Growth on (111) Nanotwinned Copper Substrate

Abstract

The microstructure of the Cu6Sn5 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 Cu6Sn5 grains formed on (111) nanotwinned Cu substrate, achieved through variations in reflow temperatures (260∘C and 300∘C) and initial Cu proportion in solder (ranging from 0 to 3.0 wt. %). At 300∘C and lower initial Cu concentrations (0 and 0.7 wt. %), irregularly arranged roof-type Cu6Sn5 grains exhibiting a pronounced {21¯1¯0} texture were observed. Conversely, typical scallop-type Cu6Sn5 grains displaying a specific preferential {21¯1¯3} texture were identified at this temperature for Cu concentrations of 1.5 and 3.0 wt. % At 260∘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 Cu6Sn5 microstructure with a designated orientation and morphology.