The circuit board rework process, regardless whether it involves eutectic or Pb-free solder, is the same. It begins by having a good thermal profile done, removing failed components, cleaning and preparing the site, and removing rust or solder residues. Next, the component is replaced with new flux and solder; re-flow is performed; and inspection is the last step.
This is where similarities end and several major differences emerge between Pb and Pb-free rework. These differences introduce a host of challenges and newer or altered practices to resolve them. With the higher temperature differences between eutectic and Pb-free solders, Pb-free rework mandates tighter processes, better thermal profiles, and newer rework practices involving greater precision provided by advanced PCB rework stations. Otherwise, a host of different rework problems can occur. Examples include the creation of a blowhole on a Ball Grid Array (BGA) ball due to the excessive heat required for Pb-free rework, BGA balls separating from the PCB substrate due to insufficient heat required for Pb-free, and/or micro-cracks occurring on a BGA and PCB caused by excessive thermal stress.
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