PURPOSE: To etch and work the pattern of a polyimide insulating layer stably with good accuracy by a method wherein an insulating film tape is formed of a polyimide resin to which a filler of an inorganic substance or the like is not added.

CONSTITUTION: A thin copper film layer is formed directly, by a sputtering method, on a polyimide film to which a filler of an inorganic substance is not added, and a composite film tape of a two-layer structure is formed. Thereby, when a polyimide opening treatment is executed, the shape of an opening by the wet etching of fine crowded via holes can be finished with higher accuracy than in conventional cases even under a proper baking condition after the development of a resist on a polyimide face. As a result, the reproducibility of the shape of the opening and the stability of the size of the opening in a wet polyimide etching operation to work a two-layer TAB are increased, and the production yield of the film tape can be enhanced.