INFLUENCE OF PACKAGE CONSTRUCTION AND BOARD DESIGN VARIABLES ON THE SOLDER JOINT RELIABILITY OF SnPb AND Pb-FREE PBGA PACKAGES
Authors: Brian Vaccaro, Dan Gerlach, Richard Coyle, Richard Company: Agere Systems, Lucent Technologies, Celestica Inc. Date Published: 9/24/2006
Abstract: A solder joint reliability evaluation was conducted for PBGA packages assembled with Pb-free SAC solder balls and paste. Test packages were constructed with and without embedded heat spreaders to study the impact of package construction on temperature cycling performance. The packages were assembled on test boards made of either standard FR-406 or a high decomposition temperature FR-4 material designed for high temperature Pb-free processing. Board pad size was one variable used to provide design data. Accelerated temperature cycling (ATC) was conducted per IPC-9701 industry test standard. All cells were tested to a minimum of 63% failure rate. Post-cycling failure analysis was conducted on representative test samples from each cell. Failure analysis included dye and pry to determine the location of the failed joints within a test net and cross sectional analysis to verify the failure mode and to evaluate the microstructure of both SAC and SnPb assemblies. In this study the SAC solder assemblies outperformed the SnPb assemblies when subjected to traditional SnPb solder joint ATC stress test conditions. This finding is consistent with other industry data, however, development of test acceleration factors for SAC solder are needed to predict performance under other thermal conditions such as field applications. The test results for SnPb packages constructed with and without embedded heat spreaders indicate no difference in ATC lifetime. However, for SAC assemblies, the heat spreader packages had a 20% longer characteristic lifetime than the packages without heat spreaders. Finally, the ATC performance of SAC assemblies was not significantly affected by differences in printed circuit board (PCB) pad size or laminate material type.