SMTA International Conference Proceedings


Authors: Lei Nie, Michael Osterman, and Michael Pecht
Company: Center for Advanced Life Cycle Engineering (CALCE) University of Maryland
Date Published: 10/4/2009   Conference: SMTA International

Abstract: In this study, Sn3.0Ag0.5Cu (SAC305) 256 I/O and 676 I/O BGAs were reballed with Sn37Pb solder balls. Different reballing methods were used in order to evaluate the effect of reballing methods on the durability of reballed BGAs. Non-reballed lead-free BGAs and reballed SnPb BGAs were assembled on printed wiring boards in a reflow process. The non-reballed lead-free BGAs were assembled with SAC305 solder paste and Sn37Pb solder paste to form the lead-free and the mixed assemblies. The reballed SnPb BGAs were assembled with Sn37Pb solder paste to form the reballed SnPb assemblies. All the assemblies were subjected to the temperature cycling test with the temperature range of -55°C to 125°C and the dwell time as 15 min.

Under continuity monitoring, the temperature cycling test revealed that the reballed BGA assemblies using different reballing methods showed similar mean cycles to failure regardless of component type. However, the mean cycles to failure for reballed assemblies was lower than that of the mixed and the lead-free assemblies. The mean cycles to failure of the mixed assemblies was better than or equal to that of the lead-free assemblies. Failure analysis revealed that the failure site in reballed BGAs was located near the interface at the component side. Although the BGAs were reballed using different solder ball removal approaches, the failure sites were the same, which meant the reballing method did not influence the crack propagation in reballed assemblies. The mixed assemblies had the same failure site as the lead-free assemblies, which was near the interface at the component side. Some large cracks were found to propagate at the board side in the survived mixed assemblies.

Key words: Reballing, mixed assembly, lead-free

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