MELTING AND SOLIDIFICATION OF THIN WIRES - A CLASS OF PHASE-CHANGE PROBLEMS WITH A MOBILE INTERFACE .2. EXPERIMENTAL CONFIRMATION

In Part I, we formulated the problem of wire heating, melting, roll-up into a ball, cooling and solidification. In this part, we describe experimental observations of the melting and solidification processes using high speed photography in an are chamber. These observations provide results for comparison with the theoretical model. In the numerical computations for the theoretical model, the heat flux from the are plasma to the wire is an input parameter. The value of this heat flux is obtained from temperature measurements made by thermocouples embedded in the unmelted wire above the ball, thus enabling comparisons between the predictions of the theoretical model and experimental observations. The heat transfer results indicate that conduction up the wire, for thin wires, is the dominant mechanism; the solidification front in the melt progresses from top downwards. The models described in Parts I and II have many applications apart from demonstrating suitable analytical and numerical procedures for treating phase-change problems with moving interfaces. The most important practical application is in semiconductor chip assembly and packaging by the ball bonding process.