Electronics in high reliability applications may be subjected to cyclic thermo-mechanical loads after being deployed for extended periods of time in harsh environment. Cyclic thermal excursion may result in solder joint fatigue leading to failure. Previous researchers have shown that exposure to high temperature for extended periods of time results in evolution of the mechanical properties of SnAgCu alloys. Deployment of leadfree electronics in harsh environment applications may result in exposure to a multitude of thermal cycles. The effect of cyclic thermal range and thermal aging on the thermal fatigue reliability has been widely documented; however the effect of the mean temperature on the thermal fatigue reliability and the strain evolution of during cyclic exposure has not been studied. In this paper, an experimental investigation has been undertaken using digital image correlation to quantify the evolution in the strain state under different mean temperatures and cyclic thermal intervals. Three different test vehicles, BGA 144, 256 and 324 were used in this study under three different test conditions 50–150°C, 0–100°C and −50–50°C. A framework to evaluate the effect of mean temperature of thermal cycle has been developed.

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