Chemical kick start for the autocatalytic formaldehyde-free electroless copper plating process

Purpose - The purpose of this paper is to examine the use of additives in formaldehyde-free copper-plating solutions with low reducing agent (RA) concentration to improve the start reaction of electroless copper deposition and to enable a copper-plating process which is more environmentally friendly. Design/methodology/approach - Different additives were investigated and their influence on the plating reaction and deposition rate was elucidated using several deposition trials. Findings - On palladium-activated base material, the additives reacted with the palladium and generated additional electrons in the initial phase of the deposition. Thus, the adequate supply of electrons from two sources (RA and additive) permits the deposition of a homogeneous and compact copper layer. Research limitations/implications - At the present time, formaldehyde is the established RA in the electroless copper metallization process used with plated through-holes. Because of its environmental impact, there is a need to replace formaldehyde. In this investigation, the more environmentally friendly glyoxylic acid is used as an autocatalytic RA. However, glyoxylic acid is more expensive and causes undesirable side reactions. 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. Originality/value - Additives can compensate for the lower RA concentration, and thus the lack of essential electrons for the copper deposition.