Rolled copper foil for flexible printed circuit and method of manufacturing the same

Abstract

A rolled copper foil for flexible printed circuits comprising, all by weight, from 0.0100 to 0.0400% of Ag, from 0.0100 to 0.0500% of oxygen, not more than 0.0030% in total of one or more elements selected from the group consisting of S, As, Sb, Bi, Se, Te, Pb, and Sn, and the balance copper, the foil having a thickness in the range of 5 to 50 &mgr;m, a half-softening temperature of 120 to 150° C., being capable of retaining a tensile strength of at least 300 N/mm at 30° C., and possessing excellent flex fatigue property and adequate softening property. The intensity (I) of the (200) plane determined by X-ray diffraction of the rolled surface after annealing at 200° C. for 30 minutes is I/I >20 with respect to the X-ray diffraction intensity (I ) of the (200) plane of fine copper powder. A method of manufacturing the rolled copper foil by a process which comprises hot rolling an ingot, repeating cold rolling and annealing alternately, and finally cold rolling the work to a foil, the annealing immediately preceding the final cold rolling being performed under conditions that enable the annealed recrystallized grains to have a mean grain diameter of not greater than 20 &mgr;m, the reduction ratio of the final cold rolling being beyond 90.0%, whereby excellent flex fatigue property and adequate softening property are achieved.