Lead-free flexible circuit board adopting single-sided gum PI copper-clad plate back line

The utility model discloses a lead-free flexible circuit board adopting a single-sided back adhesive PI copper-clad plate back wire, the lead-free flexible circuit board is made of a back adhesive PI copper-clad plate through a back copper wire, the back adhesive PI copper-clad plate comprises a copper foil layer, an adhesive layer, a PI thin film layer and a back adhesive layer, the back adhesive layer comprises a pure adhesive film layer and a release film layer, and the pure adhesive film layer and the release film layer are bonded together. The lead-free flexible circuit board comprises an upper insulating layer, a copper foil layer, an adhesive layer, a PI film layer, a pure adhesive film layer, a copper lead layer and a lower insulating layer which are sequentially arranged from top to bottom, the adhesive layer is an epoxy resin adhesive layer, and the pure adhesive film layer is an acrylic resin adhesive layer. The copper foil layer can be processed through etching, the copper conductor layer can be p