A Cocoon-Shaped Copper Plating Filling Technique for through Hole Metallization

Abstract

Recently, with the electronic products tending to be light, multifunctional and a high speed transmission, the IC substrates and printed circuit boards (PCBs) must increase circuit density and be able to accommodate a lot of elements in a single device. In order to accommodate more elements in a single device, the circuit density of PCB and IC substrate have to decrease line width and distance between conducting lines, but their overall thickness must be thinner than before. It means that the conducting via or through-hole (TH) will be small and a thin surface copper layer is necessary. In this work, we developed a copper plating formula composed of several additives to perform TH filling of an IC substrate. The results show that the copper plating formula can perform a highly selective TH filling. Copper was mainly plated in the TH and a thin surface copper layer was obtained outside the TH. The plated copper shape in the TH looks like a cocoon according to its cross-section, which can solve the dimple issue of current TH filling technology, even it can be used as copper bump for copper-to-copper connection. Keywords: Through-hole filling, Printed circuit board, IC substrate, Copper Plating, Cocoon Reference W. P. Dow, H. H. Chen, M. Y. Yen, W. H. Chen, K. H. Hsu, P. Y. Chuang, H. Ishizuka, N. Sakagawa, R. Kimizuka, “Through-Hole Filling by Copper Electroplating”, Journal of The Electrochemical Society, 2008, 155, D750-D757.