METHOD FOR ELECTROPOLISHING IRON-ALLOY LEAD FRAME

摘要

PURPOSE: To eliminate the need for copper strike plating and to directly plate a lead frame with silver in the noncontacting electropolishing device by impressing a current having a specified waveform on an electropolishing soln. of specified composition. CONSTITUTION: A material feed roll part 1, an electropolishing part 2 and a material discharge roll part 3 are successively arranged to constitute a noncontacting electropolishing device. The electropolishing soln. contains 20-40g/l sulfuric acid, 40-80g/l ammonium chloride and 0.08g/l nonionic surfactant. The iron-alloy lead frame is electropolished with the soln. at a bath temp. of 45-50 deg.C and with 0.2-8.0A/dm<2> current density. A DC current of 40-120Hz having a ripple is impressed alternately on the anode side and on the cathode side, and the time for the lead frame 17 to act as an anode is controlled to >=3.3 times the time for the lead frame to act as a cathode. Consequently, the surface of the lead frame 17 is smoothed to a high degree and directly plated with silver.