A model for solder behavior based on nonlinear dynamics has been developed by the authors (1990–1992). Supporting this study, data have been collected for near eutectic Pb-Sn solder joints using a ring and plug geometry which has been subjected to isothermal (80°C, 120°C) creep/relaxation loading ranging over a period of time up to 260 hours. Four types of relaxation data were observed: (1) smooth, low rate of unloading, (2) smooth, high rate of unloading, (3) onset of unstable racheting, and (4) onset of unstable, irregular unloading. Types (1) and (2) appear to be related to grain boundary and matrix creep, respectively. These are two creep mechanisms which have been reported in the literature. As far as we are aware, types (3) and (4) have not been previously reported by other investigators in terms related to solder instability. Therefore, our purpose is to document, in some detail, conditions under which unstable behavior has been observed. A detailed discussion is made of variables which control and measure instability including loading, fixture load cell stiffness and material type, and checks of instrumentation accuracy. This paper reports details of the experimental study regarding test specimens, test fixture, instrumentation and calibration, and environmental control. This paper provides a summary of data collection.