Two-layer flexible substrate

摘要

The invention provides a two-layer flexible substrate free of surface defects and having excellent etching characteristics and adherence to a resist. The two-layer flexible substrate has a copper layer provided on one or both faces of an insulator film without using an adhesive, wherein the surface roughness (Ra) of the copper layer is 0.10 to 0.25 mum, and wherein the average crystal grain size [of copper] is no greater than 0.8 mum at 1 mum from the insulator film in the cross-section of the copper layer. Preferably, the insulator film is a polyimide film.