Chemical 'Kick Start' for the Autocatalytic Formaldehyde-Free Electroless Copper Plating Process

摘要

The present work describes the use of additives in formaldehyde-free copper solutions to improve the start reaction of electroless copper deposition.Conventional electroless copper plating solutions contain a copper salt, one or several complexing agents, a reducing agent, a Ph adjusting agent as well as stabilizers and other additives.At the present time formaldehyde is the established reducing agent in electroless copper metallization of plated through-holes. Because of its environmental impact, there is a need to replace formaldehyde. Many alternatives have been suggested but some of them pose a greater health and safety threat than formaldehyde does and some alternatives are not economically viable.In this investigation, the more environmentally friendly glyoxylic acid is used as an autocatalytic reducing agent. However glyoxylic acid is more expensive and causes undesirable side reactions. Consequently, it leads to a rise in the price of the copper plating process. In order to keep process costs under control, the concentration of glyoxylic acid in the copper bath should be reduced without affecting the quality of the copper deposits.Therefore, additives are introduced which can compensate for the lower reducing agent concentration, and thus the lack of essential electrons for the copper deposition.On palladium-activated base material, the additives react with the palladium and generate additional electrons in the initial phase of the deposition. Thus, the adequate supply of electrons from two sources permits the deposition of a homogeneous and compact copper layer.