A flame retardant resin composition is disclosed. Cladding an Sn or Sn alloy coating with a prescribed metal continuously or discontinuously in such a way as to make the coating partially exposed inhibits the generation of whiskers by contact pressure in pressure welding, and further inhibits the generation of whiskers without impairing the solder wettability of the coating even when the cladding is not followed by heat treatment or reflowing. The method further includes determining a configuration of the electrical distribution grid including a micro-grid, the micro-grid including the one or more premises. An area setting section sets a three-dimensional detection areas respectively corresponding to the candidate workpieces.