TEMPERATURE CYCLING RELIABILITY OF REBALLED AND REWORKED BALL GRID ARRAY PACKAGES IN SNPB AND SAC ASSEMBLY
Pecht, Michael G
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In recent years, many countries banned the use of lead in select high volume electronic equipment. However, exemptions from lead-free legislation have been granted for certain products, especially those intended for high-reliability applications. Manufacturers with exemption are facing dwindling supply of lead-based components for their products. This change has left many high-reliability electronic equipment manufacturers with the choices of, mixing lead-free components in tin-lead assembly process, converting products to lead-free, or reprocessing lead-free components to comply with the tin-lead assembly process. Reballing has been used for component reclamation, but right now it offers a way to reprocess the ball grid array packages. The reliability of reballed BGA assembly needs to be determined before the implementation. Mixing lead-free ball grid array packages with eutectic tin-lead solder paste bring new challenges to the current electronic industry. The mixed assemblies with long-term reliability need to be investigated. Although rework has been implemented for decades, the impact of multiple rework process on the reliability of lead-free and mixed assemblies is still unknown. Lead-free ball grid array packages with Sn3.0Ag0.5Cu solder balls were subjected to the reballing process. Ball shear test and cold bump pull test were used to investigate the solder ball attachment strength of the reballed BGAs. Temperature cycling test was used to evaluate the temperature cycling reliability of reballed tin-lead, lead-free and mixed assemblies. The solder ball strength and the temperature cycling reliability of reballed components were independent of the reballing method. The temperature cycling reliability of mixed assemblies was equivalent to that of lead-free assemblies. Microstructure differences in lead-free, mixed and reballed tin-lead assemblies were investigated to explain the temperature cycling reliability results. Lead-free and mixed assemblies were subjected to the rework process. Temperature cycling test was used to evaluate the temperature cycling reliability of reworked assemblies. Cu over-consumption, Cu pad dissolution and thick interfacial intermetallic layer were found in the reworked assemblies. Microstructural investigation and geometry analysis were used to analyze the temperature cycling reliability degradation in the reworked assemblies after multiples rework processes.