PURPOSE: To obtain the subject foil having improved heat resistance without lowering its strength and electric conductivity by subjecting an intermediate rolling material made of Cu (alloy) to heat treatment under specific conditions into prescribed grain size and thereafter subjecting it to cold rolling again.

CONSTITUTION: An intermediate rolling material of which an ingot made of Cu (alloy) is cast, is thereafter hot-rolled and then cold-rolled into prescribed thickness is subjected to heat treatment at 600 to 800°C for 30sec to 3hr to regulate the grain size to ≥0.025mm and is thereafter cold-rolled again into foil. Furthermore, the above copper alloy is regulated to the one admixed with maximum about 1.0wt.% of one or more kinds of elements such as P, Sn, Ni, Fe, Co, Cr, Zr, Si, Mg, Ag, Mn, In, Te, B and Hf.