Fatigue damage evaluation of SMT interconnections using straddle boards

Straddle board specimens provide the ability to mechanically test and evaluate electronic components subject to actual or simulated thermal fatigue loading conditions. Although this specimen was initially intended for A to B comparisons of different joint systems, basic material behavior data can be extracted from these tests. Single-lead straddle board specimens allow for the measurement of loads and deflections on a specific joint, while maintaining the essential aspect of testing actual SMT (surface mount technology) joint/lead configurations. Fatigue tests were performed on solder joints of longitudinal and transverse loading orientations in order to separate the damage evolutions under the two conditions. Crack initiation and growth within the lead/solder interface were monitored using a video imaging system. It was found that the crack length can be directly related to the change in the rate of load drop. Tests were performed isothermally at various temperatures ranging from room temperature to 90°C. It was found that as the temperature is increased, damage occurred dramatically faster. Data from single-lead and multi-lead tests are normalized for purposes of comparison and evaluation