Corrosion Inhibitors in the Electronic Industry

Abstract The most widely used inhibitors in the electronics industry are chromates, phosphates, and silicates in chip processing and azoles in printed circuit board (PCB) fabrication. Azoles are the principal constituents of Organic Solderability Preservatives (OSPs) used on bare copper that could replace Hot Air Solder Leveling (HASL). For years HASL has been the most prevalent surface finishing process in PCB fabrication. This process is currently under scrutiny, because of safety and environment concerns (lead exposure, waste disposal), process limitations (stress, extendibility to fine-pitch device assembly), and cost. The use of azoles is a cost-effective solution to these concerns but it is also a source of new ones. Aside from being typical corrosion inhibitors, the azoles are expected to provide protection to a copper surface against thermal oxidation yet at higher temperatures inhibitors themselves are not stable. The challenge of bringing azoles to PCB manufacture has resulted in close interaction of the board shop, assembly customer, and the OSP chemistry suppliers. This paper is an overview of the relevant work in which a compromise between process demands and achievable inhibitor performance is discussed.