Reflow lead-free solder

A reflow method for a lead-free solder alloy comprising the steps of heating the solder to a first temperature which is above a liquidus temperature of the solder; cooling the solder to a second temperature which is lower than a solidification point of the solder; re-heating the solder to a third temperature which is above a solidus temperature of the solder and below the liquidus temperature of the solder so that the solder is transferred from a solid state to a liquid + solid state, in which a part of the alloy phase has become liquid, wherein the primary solidification phase is relatively deformable grains which remain fixed; and cooling the solder to a fourth temperature which is below the solidification point of the solder, wherein the stiffness caused by a sub-cooling in the first cooling step in the lead-free solder can be reduced by the second heating or eliminated.