Symposium Conference Proceedings


Authors: Gregory Henshall, Michael Fehrenbach, Chrys Shea, Quyen Chu, Girish Wable, Ranjit Pandher, Ken Hubbard, and Ahmer Syed
Date Published: 5/19/2011   Conference: Symposium

Abstract: Some ball grid array suppliers are migrating their sphere alloys from SAC305 (3% Ag) or SAC405 (4% Ag) to alloys with lower silver contents. There are numerous perceived reliability benefits to this move, but process compatibility and thermal fatigue reliability have yet to be fully demonstrated. The current study has been undertaken to characterize the influence of alloy type and reflow parameters on low-silver SAC spheres assembled with backward and forward compatible pastes and reflow profiles. This study combines low-silver sphere materials with tin-lead and lead-free SAC305 solder pastes under varied reflow conditions. Solder joint formation and reliability are assessed to provide a basis for developing practical reflow processing guidelines and to assist in solder joint reliability assessments. This is the sixth report in a series being published as results become available, and presents results of the thermal cycling portion of the test program. Thermal cycling conditions include both 0 to 100oC and -40 to 125oC, with 10 minute dwell times. The accelerated thermal fatigue reliability of Pb-free solder joints with varying Ag and “micro alloying” element concentrations is compared with that of 100% Sn-Pb joints for four different package types. Further, the impact of thermal cycle conditions on the rank order of the reliability for the different solder joint compositions is presented. The implications of the data regarding the efficacy of using BGAs balled with low Ag alloys, and areas for future work are discussed. Key words: low-silver alloys, thermal fatigue, solder joint reliability, Pb-free alloys, SAC alloys

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