RESIN FILM AND METHOD OF MAKING SAID FILM.

摘要

A resin film for mainly making a flexible printed circuit board and a method of making the film. When a copper foil (2) is etched in a specified pattern after heat-bonded to a resin film (1) in order to make a flexible printed circuit board, said board undergoes a dimensional variation. For the purpose of reducing such dimensional variation, a ratio (a/b) of a linear expansion coefficient (a) of the resin film (1) in the mechanical feeding direction (MD direction) to that (b) in the direction (TD direction) perpendicular to said mechanical feeding one is set at 0.2 or more but less than 1.0, and the linear expansion coefficient in said mechanical feeding direction (MD direction) is set at 0.4 to 2.0 x 10<-5> DEG C<-1>. As a resin film, a polyimide film including 90 % or more of identity period represented by a specified general formula is used. Further, for making said resin film, the film (1) is stretched 1.0 to 1.5 times in the mechanical feeding direction (MD direction) and 0.5 to 0.99 times in the direction (TD direction) perpendicular to the mechanical direction.