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Thermal Cycling Reliability of Sn96.5Ag3.0Cu0.5 Solder Assembled with ENIG and OSP Pad Finishes
Keywords: Lead free, OSP and ENIG, Isothermal aging
Electroless nickel immersion gold (ENIG) and Organic solderability preservative (OSP) are commonly used board finishes among the electronic packaging community. The difference in these two finishes 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. Elevated temperature aging affects the bulk and interfacial microstructure of the solders. These changes in interfacial and bulk microstructure due to above factors might affect the solder reliability under thermal fatigue. This paper aims to study 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 pads. 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 100oC for 24 hours acted as the controls for the experiment. Thermal cycling tests (-55oC to 125oC) were carried out on the aged solders and thermal fatigue life was compared. Failure analysis was carried out on the failed components to determine the failure sites and microstructural evolution as a result of thermal cycling.
Preeti Chauhan, Graduage Student
University of Maryland
College Park, MD
USA


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