A leadframe of a single frame structure for supporting leads on IC chips. The leadframe is made of a high-strength, high-electroconductivity copper alloy. The copper alloy is produced by preparing an ingot of a copper alloy of 0.05-0.40 wt. % Fe, 0.05-0.40 wt. % Ni, 0.01-0.30 wt. % P, and optionally a total of 0.03-0.50 wt. % of either Sn or Zn or both and a total of 0.05-0.50 wt. % of at least one element of Ag, Co, B, Mn, Cr, Si, Ti and Zr, with the balance being Cu and incidental impurities, heating the ingot to 800 to 950.degree. C. and hot working the ingot to a reduction ratio of 50% or more, quenching the hot worked material from 600.degree. C. or above down to 300.degree. C. or below at a cooling rate of at least 1.degree. C./seconds, heat treating the quenched material at 380 to 520.degree. C. for 60-600 minutes without cold working, and subsequently carrying out cold working and heat treating at 450.degree. C. or below, whereby an Fe--Ni--P system intermetallic compound is precipitated in the Cu matrix as uniform and fine grains not larger than 50 nm.