A study on the effects of chromium plated substrates and additives on copper electrodeposit for Ultra Thin Copper Foil Process

Abstract

Copper electroplating from aqueous solution to form reliable, highly conductive current paths on PCBs (printed circuit boards) and associated devices is a wide-spread and important process in the electronics industry. One application of the electroplating process is making thin copper foil for printed circuit boards by using electroforming technique. Recently the circuit density of PCB is getting higher and PCB makers need to make a fine circuit patterned PCB. UTC (Ultra Thin Copper foil; copper foil thinner than 9 ∼ 12 ㎛) meets the requirement of PCB industry. In UTC making process, copper is electrodeposited on the foil substrate (so called carrier) covered with a parting agent or release layer on which the quality of copper electrodeposits is determined. But nucleation and growth process on parting agent, like chromium electrodeposits, and suitable additive conditions for high strength copper electrodeposits are not yet reported. In this work, nucleation and growth mechanisms of copper on as-plated chromium electrodeposits and on electrochemically surface treated chromium deposits in copper sulfate electrolytes were studied by using several electrochemical analyses. Optimum additive concentrations of copper sulfate electrolytes for UTC application were also investigated.

A. Nucleation and growth of copper deposit on electroplated chromium layers The influence of chromium deposition time on copper nucleation and growth behavior was examined by potential step tests in copper sulfate electrolyte, and the results were discussed with Scanning electron micrographs, Auger electron spectroscopy (AES), and electrochemical impedance spectroscopy (EIS) results. It was found that the initial nucleation and growth of copper on the electroplated chromium layers are controlled by the deposition time of chromium layer. The mechanism of nucleation and growth of the copper deposits was analyzed according to the theories developed by Thirsk and Harrison using the pot...