Presented at the 55th Electronic Component and Technology Conference, June 2005

Effect of Stress Relaxation on Board Level Reliability of Sn Based Pb-Free Solders

S. Yoon, Z. Chen, M. Osterman, B. Han and A. Dasgupta
CALCE Electronics Products and Systems Center
Department of Mechanical Engineering
University of Maryland
College Park, MD 20740


Abstract The thermal fatigue data of two Sn-based Pb-free solders (Sn95.4/Ag3.9/Cu0.7, Sn96.5/Ag3.5) are presented. The test vehicles (LCCC mounted on FR-4 PCB) are subjected to various thermal cycling conditions; a constant temperature excursion (T = 100C) with different cyclic mean temperatures and dwell times. The results are compared with the results of Sn63/Pb37. The results show that the two Pbfree solders outperform the SnPb solder at the lower cyclic mean temperatures, while the SnPb solder has a longer fatigue life at the higher cyclic mean temperatures. Reliability of the Pb-free solders has much stronger dependence on the cyclic mean temperature. The results are analyzed systematically to investigate the effect of stress relaxation at the peak temperature on the fatigue life.

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