Preeti Chauhan, Michael Osterman, and Michael Pecht
CALCE Electronic Products and Systems Center
University of Maryland
College Park, MD 20742
An experimental study was conducted to examine the effect of elevated temperature isothermal aging on thermal cycling reliability of lead-free solders. Test specimens were assembled using Sn-finished 2512 resistors soldered onto OSP and ENIG-finished copper. The difference in these two finishes post assembly comes primarily from the Sn/Ni and Sn/Cu interfaces in ENIG and OSP finishes respectively. The presence of these different interfaces in ENIG and OSP and Au in the solder bulk in ENIG finish is expected to govern the solder bulk and interfacial solder-Cu pad interactions. Lead-free solder SAC305 was examined and its thermal fatigue reliability was compared with that of SnPb solder. Test specimens were aged at 100°C for 100, 500 and 1000 hours. Specimens aged at 100°C for 24 hours acted as the controls for the experiment. Test specimens were subjected to a temperature cycle test condition of -55°C to 125°C and the differences in isothermal aged tests sets were examined. Failure analysis was carried out on the failed components to determine the failure sites and microstructural evolution as a result of thermal cycling.
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