The effect of transition layer on the strength of nanotwinned copper film by DC electrodeposition

Nanotwinned copper is reported to have excellent strength, hardness and conductivity. So nanotwinned copper is a promising material to replace conventional coarse-grain or nano-grain copper using as redistribution layer (RDL) in the electronic packaging industry. In this study, the direct current (DC) electrodeposition was used to prepare nanotwinned copper films with a high-acid and high-salt plating solution. Within these nanotwinned copper films, a 2-4 μm thick equiaxed-grain transition layer was formed between the nanotwinned region and substrate as observed by scanning electron microscope (SEM), which takes a proportion ranging from 9.7% to 46.2% of total thickness within the film. It was founded that the corresponding tensile strengths of these films is closely related to the thickness of transition layer. In detail, the smaller the proportion of the transition layer, the stronger tensile strength of the film can be obtained.