Allowable copper thickness for fine pitch patterns formed by a subtractive method

The subtractive method is widely used to produce high‐density PWBs. It is generally accepted that a pattern pitch of 100 microns or less cannot be achieved by the subtractive method because of the thickness of the copper layer to be etched. We report here on experiments to investigate the relationship between the pattern pitch of a circuit formed by the subtractive method and the required thickness of the copper layer. We have also determined the allowable thickness of the copper layer, plating layer, and copper foil layer for achieving a pattern pitch of 100 microns (L/S = 50/50 microns) or less.