Patent ID: 7459047

Claim:
A method for preparing a flexible metal foil/polyimide laminate, comprising: applying a polyamic acid varnish onto a very thin copper foil having a thickness of up to 9 μm supported on a carrier, semi-drying the varnish until a solvent content of the varnish becomes 40 to 100% by weight based on varnish solids, laminating a polyimide film to the varnish-coated copper foil using a hot roll press, and heat treating the laminate for removing the residual solvent in the varnish and imidizing the polyamic acid in an atmosphere having an oxygen concentration of up to 2% by volume, wherein a polyimide adhesive layer resulting from the imidization of polyamic acid has a thickness of up to 6 μm, the sum of the thickness of the polyimide film and the thickness of the polyimide adhesive layer is up to 25 μm, and the polyimide adhesive layer has a glass transition temperature of higher than 400° C.