Rework and reliability of QFP and BGA lead-free assemblies

As the implementation of lead-free assembly gains momentum in the electronics industry, the rework process will inevitably come into the spotlight as process fall-outs are encountered. Lead-free assemblies usually require higher temperatures than those with eutectic tin-lead solder. During the rework process, the components and the PCBs are repeatedly subjected to high temperatures during component removal, redressing, and replacement. The qualification of lead free assemblies would not be complete without an understanding of the performance of reworked components. In this study, lead-free assemblies of QFPs (176 pins) and BGA packages (81 balls) were used as test vehicles for rework trials. QFP176 reworking was carried out manually using hot air soldering equipment and a soldering iron. Investigations were carried out simultaneously by two different groups with different sets of tools, techniques, and skills. Pull-strength tests were carried out to assess reworked solder joints before and after thermal aging for 750 cycles in air with conditions of -40°C to 125°C. A slight degradation in pull strengths was recorded on reworked parts after temperature cycling, but did not represent a reliability hazard.