Fluororesin base material, printed wiring board, and circuit module

A printed wiring board comprising a fluororesin base material and a metal layer,

• the fluororesin base material containing a fluororesin layer and a modified layer,
• the metal layer being disposed on the modified layer,
• the fluororesin layer containing a fluororesin as a main component,
• a content of the fluororesin in the fluororesin base material being 90 mass % or more based on a total mass of the fluororesin base material,
• the fluororesin containing a tetrafluoroethylene-hexafluoropropylene copolymer,
• the modified layer being disposed on a partial region of a surface of the fluororesin layer in the fluororesin base material,
• the modified layer containing a siloxane bond and a hydrophilic organofunctional group,
• a surface of the modified layer having a contact angle of 90° or less with pure water,
• the surface of the fluororesin layer not having the modified layer having a contact angle of 95° to 130° with pure water, wherein
• a C atom in radical form of the fluororesin is covalently bonded to the siloxane bond (Si—O—Si) formed with a silane coupling agent via another atom or atomic group,
• the fluororesin base material has an optical transmittance of 50% or more at a wavelength of 600 nm, and
• the surface of the modified layer has a mean surface roughness Ra of 4 μm or less.