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Effect of Extended Dwell Time on Thermal Fatigue Life of Ceramic Chip Resistors
Keywords: Solder Joint Reliability, Lead-free Solders, Dwell Time
The effect of temperature cycling test parameters such as dwell and ramp times, mean cyclic temperature and temperature range, on the fatigue life of solder interconnects is critical for qualification and reliability testing. Upon achieving complete stress relaxation, further increase in dwell time does not decrease the fatigue life of solder interconnects. Studies have shown that an increase in dwell time beyond a certain limit (10-20 minutes) has no effect on the fatigue life of lead-based solders. Stress relaxation duration is longer in lead-free SnAgCu and SnAg solders than in lead-based solders resulting in higher creep damage accumulation, thereby reducing the fatigue life of solder joints. Experimental data for accurate modeling of the effect of extended dwell time (beyond 60 minutes) on the temperature cycling reliability of lead-free solders is limited. In this study, 2512 ceramic chip resistors soldered onto FR4 board using both common lead-free and eutectic SnPb solders are subjected to temperature cycling profiles with 10 and 120 min dwell time durations. Resistors with standard and narrow pads are compared to study the effect of pad size on fatigue reliability. For lead-free solders, the extended dwell time resulted in a decrease in thermal fatigue life, except for in narrow pad resistors soldered using SN100C solder. Extended dwell may be have annealed the SN100C solder, making it more robust to solder fatigue. The effects of absence of silver and presence of nickel in SN100C solder will be addressed in the analysis of failed solder interconnects.
Elviz George, Research Assistant
Center for Advanced Life Cycle Engineering
Arlington, VA
USA


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