The Effect of Testing a Copper Wire and a Copper Wire Coated with SnPb Solder using a Wetting Balance Machine

A copper surface chemically passivated using some form of flux has been suggested as providing samples of different but reproducible degrees of solderability. The importance of closely controlling the preparation, and cleaning of the copper to obtain reproducible solderability is of high importance to ensure accurate and repeatable results when using the Wetting Balance Machine. After completing a capability study of the Wetting Balance machine prior to conducting any experiments, 20mm lengths of copper wire were used to assess the effect of soldering directly onto a copper wire surface compared with soldering onto a copper wire surface coated with tin/lead (SnPb) solder paying particular attention to the responses Fmax, maximum force reached during the test, TFmax, time to reach maximum force, T2/3 Fmax, time to reach two thirds of maximum force, Tb, time to reach buoyancy, and finally Ta, Time to reach the zero line of the x-axis. For the benefit of this investigation, 20mm lengths of the same reel of 0.9mm diameter insulated copper wire were used in order to minimise as much as possible any variances. For each 20mm length of copper wire used, an initial dip of the specimen into the solder bath, calculating the aforementioned responses, was followed by a second dip using the same initial copper wire but this time it had a coating of tin/lead solder from the first dip and again the relevant responses calculated using the Wetting Balance machine. A comparison of each response was done to compare the first dip with on a Cu surface and the second dip with the SnPb coating in order to assess the effect of thermal conduction.