Long-Term Dynamic Stability of the Interfacial Cu₆Sn₅ Texture in SAC305/Cu Joints by Laser Jet Solder Ball Bonding...

Green and energy-efficient laser soldering technology has been recently developed in electronic packaging to overcome the limitations of conventional soldering. In this study, different sized Sn-3.0Ag-0.5Cu/Cu ball grid array joints were fabricated by laser jet solder ball bonding and the joint size effect on the morphology and texture of interfacial Cu₆Sn₅ grains during subsequent reflow was investigated. It was found that prism-like Cu₆Sn₅ grains preferred to form with increasing joint size, and those in the large-sized joints (760 μm) also exhibited a strong ⟨112̅0⟩ texture and low misorientation frequency of 70° and 90°. The high bonding temperature provided large nucleation energy (ΔG), and the (110)Cu pad provided favorable nucleation and growth conditions for Cu₆Sn₅ grains, which copromoted the formation of the prism-like oriented grains. The evolution mechanism of the above peculiar morphology and texture was revealed based on the rapid growth along the [0001] direction (c axis) and grain boundary migration of the Cu₆Sn₅ grains. For the large-sized joints, the ⟨112̅0⟩ texture remained dynamically stable to perform as roof-like grains through a merging process. While, for the small-sized joints (400 and 600 μm), the originally formed texture gradually disappeared during the subsequent reflow, which was attributed to the gaps among the short rod-like Cu₆Sn₅ grains. These gaps preserved the misorientations of 70° and 90°, leading to the development of large needle-like or prism-like grains Cu₆Sn₅ with random orientations.