The use of lead-free materials in rework leads to more stringent demands for technology. The main characteristics of lead-free solders are reduced self-alignment and wetting effect, as well as higher melting temperature. This results in a smaller rework process window and precise thermal management becomes more critical. Higher reflow temperatures create a narrow process window with risk of component and board damage if not properly managed. Process temperatures in excess of 220C are reaching the maximum-allowed limit for most components and must be carefully regulated. Rework systems must be capable of managing this limit in a repeatable manner.

Lead-free alloys do not produce the same “self-aligning” characteristics normally seen with tin-lead soldering. Therefore, initial alignment and subsequent placement accuracy of the component in lead-free solder takes on a higher importance. No longer will the physics of surface tension in molten solder be a substitute for placement accuracy.

Additionally, as components get smaller, component proximity becomes an issue. Nozzles must be able to fit between components. Systems need to be able to rework one component without disturbing the neighboring components. Proven lead-free rework systems will have precise temperature and gas flow control. It is this same technology that aids in rework of smaller components on more densely populated boards.

Many companies are using older rework systems that do not have these precise controls. Due to the lead-free movement, customers will need to carefully evaluate their current systems for compliance.