In this study, we examined how to lower the reflow temperature using a method in which oxide film is removed by generating hydrogen radicals in a vacuum. As a result, the joint strength obtained was almost equal to that of Sn-37Pb solder. To confirm the possibility of reflow processes without flux, the reduction effect of hydrogen radicals and SnO2 were considered. We increased the reflow temperature up to 10•Ž higher than the melting point, after removing the oxide film which was previously melted at a temperature lower than the melting point by generating hydrogen radicals without using flux. As a result, the same levels of surface properties and joint strength were obtained, and void creation was suppressed. Therefore, we conclude that introducing hydrogen radicals makes it possible to reflow process lead-free solders such as Sn-3.0Ag-0.5Cu without using flux and without void creation. In addition, this method was applied to bump formation reflow.