Lead-free solder pastes require higher reflow temperatures and tighter process controls than standard tin-lead solder.
The reflow process window for tin-lead solder is relatively wide. The melting point of tin-lead solder is 183 C. The lower temperature limit for reflow is 200 C. The upper limit is generally 235 C, which is the maximum temperature that most components can be exposed to. These high and low temperature limits provide a process window of over 30 C.