Study Of Electrodeposition Of Ultrathin Peelable Carrier-attached Copper Foils

Copper foil is a key conductive material used in manufacturing printed circuit boards (PCBs). As PCBs become multi-layered, thinned, densified and accelerated, the production of ultrathin electronic copper foils with low profile, high strength and high ductility is more difficult and pressing. Hence the preparation and peeling of ultrathin copper foils have become a recent research focus in copper foil industry. The purpose of this thesis is to seek new single-or multi-component organic agents, which can constitute an efficient release layer on a carrier foil to electrodeposit an ultrathin copper foil on its surface. The desired release layers should be formed simply by immersing the carrier foil in an aqueous solution containing the organic agent (s) for a short time, and the obtained ultrathin copper foils are expected to have a minimum peelable thickness not beyond 4 μm.Three organic agents were selected for forming the release layer, including benzotriazole (BTA), a thiazole compound MAT, and a mixture of MAT and phytic acid, amoung which BTA was studied only as a contrast agent. The ultrathin copper foils were galvanostatically deposited on a 35 μm thick carrier copper foil with the preadsorbed organic release layer. The processing parameters were optimized, including the concentration of the organic agents, the adsorption time, the current density, temperature and deposition time. The surface morphology of the ultrathin copper foils was characterized using optical and scanning electron microscopy. The effect of the release layers on the electron transfer kinetics of copper deposition was studied by Tafel and electrochemical impedance methods.Results show that the uniformity and peelability of the ultrathin copper foils are highly dependent on the nature and adsorption amount of the release layers, current density and temperature; and the three release layers show great difference in their impact on the electron transfer kinetics of copper deposition. The BTA release layer has the largest resistance to the redox reaction of copper. The BTA concentration required for forming an effective release layer is as high as 10 gL-1. A minimum peelable thickness of 8 μm was obtained for the copper foil prepared with the BTA release layer. The MAT release layer shows a resistance to the redox reaction of copper much less than the resistance of BTA. The MAT concentration required for forming an effective release layer is as low as below 1.0 g-L-1. The prepared copper foil showed a smooth and layered crystal surface, with a minimum peelable thickness down to 4 μm. Introduction of phytic acid to the MAT-phytate composite layer resulted in a great increase in the resistance to the copper deposition reaction, and a further decrease in the minimum thickness of copper foil down to 3 μm. In the presence of phytic acid, however, the copper foil surface topography is very sensitive to the magnitude of current density; the surface of copper foil became coarse and loose with the increase in current density up to 6.0 A-dm-2. In short, MAT as a release layer is significantly superior to BTA; and phytic acid, as a chelating agent of Cu2+ ions, shows a preliminary effect on reducing the thickness of copper foils.