Cost-Effective Alternatives to Palladium Activation – A Study on Autocatalytic Electroless Copper Deposition

Abstract

Electroless copper plating is the most important and critical step for through-hole metallization of printed circuit boards. Conventional electroless copper solutions contain formaldehyde as the standard reducing agent. Due to the toxic nature of formaldehyde, there is a need to change to a reducing agent that is more environmentally friendly and safer to use. Many reducing compounds have been proposed to replace formaldehyde. For example, glyoxylic acid has been described in the literature as an especially attractive alternative because of its relative safety. In preparation for electroless copper plating, substrates are typically catalyzed by the adsorption of palladium. However, a change in the reducing agent can also lead to a change in the activation process, primarily because there is no single metal that appears to be a good catalyst for the oxidation of all reducing agents that have been employed for electroless deposition. In the present study, electrochemical measurements were carried out in order to obtain information about the catalytic activity of copper, silver, nickel and palladium in the oxidation reaction of formaldehyde as well as glyoxylic acid. Metals with high catalytic activity for each reductant oxidation can be determined by using cyclic voltammetry. These metals are candidates for an improved activation process. Electrochemical measurements showed that palladium does not have the highest catalytic activity of all tested metals. Therefore, more cost-effective, alternative metals were examined as catalysts for electroless copper plating reactions. The paper presents the results of a PhD thesis, which included tests on cheaper alternatives to palladium for activation of autocatalytic electroless copper deposition. It also includes production scale studies and conclusions on possible replacement of formaldehyde as a reducing agent for electroless copper deposition.