Effect of pulse off time on microstructure and properties of twinned copper films by pulse electrodeposition

Due to the existence of nano twins, nanotwinned copper has excellent mechanical and electrical properties, which can effectively reduce the formation of Kirkendall holes. So it has a wide application prospect in electronic packaging and other fields. In recent year, vertically twinned copper was proposed, however, its properties was seldom reported. Therefore, in this paper, a series of vertically grown twin copper were prepared. Different microstructure and properties were obtained by changing the duty cycle of pulse parameters. The diffraction peak intensity of different coatings was measured by X-ray Diffraction (XRD). The surface topography and cross-sectional microstructure of the coating before and after annealing test (250 ℃ , 1h) were characterized by Focus Ion Beam (FIB). It was found that the surface morphology of the coating depended on the parameter of t
off
. Compact and smooth surface was obtained with longer t
off
. When the proportion of (220) crystal orientation increased, the vertical twin lamella seem to be more denser. Dynamic mechanical analyzer (DMA) was used to test the mechanical properties of these coatings with different structures. The best tensile strength estimated at 265MPa with a elongation at 3.619% was obtained when t
off
was 1s. Besides, these copper films were easy to recrystallized, grain growth within these coating was observed after annealing at 250 ℃ for 1h. This study provides significant insights to controllable preparation of copper films in different microstructure.