For solid connections
Soldering is a thermal process for the joining of materials with a substance-to-substance bond by creating a liquid phase using melted solder or by diffusion at the boundary surfaces. This creates a surface alloy, but the workpiece is not melted at depth. After solidification of the solder, a substance-to-substance bond similar to welding is produced.
Resistance soldering is used in particular for Cu materials and here, for example, for switch contacts with a fusion surface larger than 4 mm². Resistance soldering requires a solder additive, usually L-Ag15P.
More info about Bihler's resistance welding processes