Influence and mechanism of ultrafast laser-textured Cu substrate on wetting behavior of SAC305 solder

Periodic arrays of grids, micro-cones, and grooves were successfully fabricated on Cu substrate using ultrafast laser technology. The wetting behavior of SAC305 solder on micro-nano structured Cu substrates was investigated, and the influence mechanism of superficial micro-nano structure was discussed using classical wetting model and molecular dynamics (MD) simulation. The results indicate that compared to polished surface, all the superficial micro-nano structures on Cu substrate improve the wettability and wetting kinetics of SAC305 solder. Especially, grid structure shows the most significant improvement, and the effect is further enhanced with the increase of processing depth. When the processing depth of grid structure is 25 μm, the smallest wetting angle of 15.1° and wetting equilibrium time of 29 s were achieved. The wetting process of SAC305 solder on Cu substrate is composed of rapid reaction stage, stable diffusion state, and equilibrium stage. Rⁿ ∼ t relationship curve reveals that the influence of micro-nano structure on wetting kinetics mainly occurs in the rapid reaction stage. The enhancement of wettability and wetting kinetics from superficial micro-nano structure can be attributed to the introduced extra capillary force and the improved atomic diffusion rate on the wetting interface.