NOVELTY - The back film comprises a base layer such as polyethylene terephthalate layer and polyethylene foaming layer located on a base surface of ethylene vinyl acetate glue film layer, a polyethylene layer (4), a silicon film forming layer, a polymer adhesive layer, a fluorine coating (6), a fluorinated siloxane film forming layer (7), and a silicon-titanium film layer. A thickness of the base layer is 0.1-10 mm, a thickness of the ethylene vinyl acetate film layer is 0.01-0.1 mm, a thickness of the polymer adhesive layer is 0.005-0.01 mm, and a thickness of the polyethylene layer is 0.012-0.05 mm.    USE - The back film is useful in a solar battery.    ADVANTAGE - The back film exhibits high humidity resistance and excellent bonding strength, durability, corrosion resistance and water vapor barrier performance.    DETAILED DESCRIPTION - The back film comprises a base layer such as polyethylene terephthalate layer and polyethylene foaming layer located on a base surface of ethylene vinyl acetate glue film layer, a polyethylene layer (4), a silicon film forming layer, a polymer adhesive layer, a fluorine coating (6), a fluorinated siloxane film forming layer (7), and a silicon-titanium film layer. A thickness of the base layer is 0.1-10 mm, a thickness of the ethylene vinyl acetate film layer is 0.01-0.1 mm, a thickness of the polymer adhesive layer is 0.005-0.01 mm, a thickness of the polyethylene layer is 0.012-0.05 mm, and a thickness of the fluorinated siloxane film forming layer and the silicon film layer (5) is 0.01-5 microns. The fluorinated siloxane film forming layer is formed using a plasma silicon fluoride. The fluorine-containing coating is tetrafluoroethylene base film layer or vinyl chloride film layer, and has a thickness of 5-200 microns.    DESCRIPTION OF DRAWING(S) - The diagram shows a schematic view of a back film.    Substrate (1)    Polyethylene layer (4)    Silicon film layer (5)    Fluorine coating (6)    Fluorinated siloxane film forming layer. (7)