Wetting Balance Test of Tin-Based Solder Alloys: Effect of Oxide Removal on Wetting Performance

This study investigates the influence of the dwell time between the mechanical oxide removal from the surface of the molten solder by a scraper and the initiation of the wetting balance test on the wettability of copper. This prolongation could potentially influence soldering performance and has not been studied yet. Copper wire with a cross-sectional area of $1.5 \mathrm{~mm}^{2}$, rosin-based flux, and three different lead-free solder alloys ($\mathrm{SnAg3Cu0.5}, \mathrm{SnAg4}$, and SnCu 3) were utilized for this experiment. Our findings revealed that the oxidation of the solder surface during the time delay of up to $\mathbf{1 0}$ minutes has a negligible effect on the wettability of the copper for all of the utilized alloys regardless of the flux application. However, when no flux was applied to the Cu wire, this time delay affected wetting behavior, particularly of SnAg 4 and SnCu 3 alloys, which exhibited heightened surface oxidation sensitivity in contrast to $\mathbf{S n A g 3 C u 0. 5}$. These results demonstrated that it is not necessary to extensively monitor the cleanliness of the molten solder surface during the wetting balance test, nor in processes like wave soldering.