Composite film, rigid flexible printed circuit board, and electronic device including same

A rigid flexible printed circuit board (RFPCB) comprising:

• a composite film;
• a flexible area on at least a first portion of at least one surface of the composite film;
• and
• a rigid area on at least a second portion of the at least one surface of the composite film,
• wherein the composite film comprises:
• a base film layer;
• and
• a first metal thin film layer on a first surface of the base film layer;
• and
• a second metal thin film layer on a second surface of the base film layer, opposite to the first surface,
• wherein the first metal thin film layer and the second metal thin film layer comprise a soft etching-treated area and at least one oxide surface-treated area, and
• wherein the soft etching-treated area has a surface roughness that is different from a surface roughness of the at least one oxide surface-treated area.

A method comprising:

• obtaining a composite film that includes:
• a base film layer;
• a first metal thin film layer on a first surface of the base film layer;
• and
• a second metal thin film layer on a second surface of the base film layer, opposite to the first surface;
• and
• treating a surface of the first metal thin film layer and the second metal thin film layer such that the first metal thin film layer and the second metal thin film layer include a soft etching-treated area and at least one oxide surface-treated area, and
• wherein the soft etching-treated area has a surface roughness that is different from a surface roughness of the at least one oxide surface-treated area.