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The effects of substrate roughness on wettability of non-reactive wetting and compound forming wetting systems are investigated by the sessile drop technique at high temperature. The AgCu28/copper system is selected in the presented study. It is found that the existence of roughness promotes wetting and spreading significantly. With the increase of roughness (R_a), the contact angle decreases sharply first and then approaches to a constant value, while the drop base radius increase linearly with R_a. Spreading of the liquid alloy on rough surface combined two modes: on top of the rough surface and inside the capillary grooves. The wetting kinetics for both modes follow the power law relationship. The driving force of flowing on the top of the rough surface follows the basic Young’s equation, while an additional driving force of capillary force exists when flow inside the micro v-grooves, leading to a decrease in final contact angle and consequently a better wettability.