The analysis of the withdrawal force curve of the wetting balance curve

In order to evaluate the withdrawal force curve that is shown in a typical wetting balance curve, a number of wetting balance tests were conducted in this study using Sn-37%Pb solder and copper plate samples whose shapes and immersion depths were varied for the purpose of this study. In the shape-effect experiment using vertical copper plate samples whose bottom corners were cut out in rectangles, a new step-like section appeared in the downfall segment of the wetting balance curve. According to the depth-effect experiment, the amount of time needed for the curve to reach the pinnacle of the withdrawal force curve increased in proportion to the immersion depths of the plates while the span of time taken for the drop of the curve was not affected by the depth. The decrease of the maximum measured force under the condition of a deeper immersion depth is attributable to the buoyancy force that also increases as the immersion depth gets deeper. It can be concluded from the results that: 1) the ascending profile of the withdrawal force curve in the typical force-time curve represents the sliding of solder on plates; 2) the highest point on the withdrawal force curve stands for the state in which the sliding solder meets the bottom corners of a normal vertical plate.