Flexible printed circuit board and method for producing the same

A method for producing a flexible printed circuit board including a base film and a wiring layer disposed on at least one surface of the base film and having a plurality of wiring lines,

• the wiring lines having an average line width of 30 μor less and an average spacing of 30 μm or less,
• the wiring lines having a copper-based plating layer,
• the copper-based plating layer having an electrical resistivity of more than 1.68×10−8 Ω·m,
• the method comprising:
• a step of stacking a conductive underlying layer on at least one surface of the base film;
• a step of forming a resist pattern on a surface of the conductive underlying layer;
• a step of forming a copper-based plating layer in an opening of the resist pattern on the conductive underlying layer by electroplating in a plating solution;
• and
• a step of removing the resist pattern and a region of the conductive underlying layer, the region not having the copper-based plating layer thereon,
• wherein the plating solution contains a first organic compound, a second organic compound, and a third organic compound,
• the first organic compound includes disodium 3,3′-dithiobis(1-propanesulfonate),
• the second organic compound includes polyethylene glycol, and
• the third organic compound includes a nitrogen-containing organic compound.