Formation and Growth Mechanism of Laminar Cu6Sn5 with Ultrafine Grains on Nanocrystalline Cu by Interfacial Reaction with Sn

Abstract Cu 6 Sn 5 intermetallic compound (IMC) formed at Sn/polycrystalline Cu interface after liquid–solid reaction generally presents scallop‐like morphology and tends to ripen into large‐sized grains with texture feature. In this paper, the formation of laminar Cu 6 Sn 5 on nanocrystalline (NC) Cu by interfacial reaction with liquid Sn is reported. The laminar Cu 6 Sn 5 consists of stacked ultrafine grains, thickened in the manner of “nibbling” the NC Cu and shows randomly distributed orientations. With extended reaction time, the top Cu 6 Sn 5 grains that are exposed to the liquid Sn transform into long‐rod‐like grains all along their <0001> direction, while the bottom Cu 6 Sn 5 grains remain laminar and ultrafine. The formation and growth mechanism of the novel laminar Cu 6 Sn 5 at the Sn/NC Cu interface as well as that of the rod‐like Cu 6 Sn 5 are revealed from the aspects of atomic diffusion, nucleation, and grain merging. It is also found that the Cu 3 Sn IMC generated at the laminar Cu 6 Sn 5 /NC Cu interface is much thinner than that at the classic scallop‐like Cu 6 Sn 5 /polycrystalline Cu interface, showing no obvious formation of Kirkendall voids.