Reflow soldering of circuits on heat sensitive materials

Reflow soldering consists of two basic processing steps. The first step is to assemble the parts to be joined, including the placement of sufficient solder where appropriate to make the interconnections. When soldering circuits to terminals this solder is normally in the form of doughnuts, called solder preforms, which are placed over the terminals. The second step is to provide a thermal heating cycle which will melt or "reflow" the prepositioned solder to join the metallic elements together. If all the parts in the assembly can withstand soldering temperatures, the assembly can be heated to a uniform temperature by convective heating utilizing fluids such as air or polyethylene glycol.