Corrosion behaviors of Co, Co/Pd, and Co/Pd/Au surface finishes

Background: Corrosives substance in polluted air causes severe reliability issues for electronic devices. One of the critical purposes of a surface finishing layer on a printed circuit board is to increase the corrosion resistance of the conductive Cu layers. However, the currently available technologies for consumer products have difficulties meeting these requirements. Methods: In this study, ultra-thin single layer Co, multilayer Co/Pd, and Co/Pd/Au are used to investigate the ability of corrosion resistance. The concentrations of the corrosive SO₂ gas used higher than those of the conventional methodology (in ppb level) to intentionally from corrosion products that are sufficiently large for meaningful composition analyses. Significant findings: The results show that a 200 nm Co, 200 nm Co/100 nm Pd, and 200 nm Co/100 nm Pd/100 nm Au can sustain a corrosive ambient environment with 150 ppm SO₂. In an extremely high concentration of 1500 ppm SO₂, the surface finishing layers failed to protect the Cu beneath. The failure analysis provides an understanding of the relationship between the microstructure and the atomic diffusion path. The corrosion mechanism is confirmed by electrochemical measurements. This study clearly confirms that Co is a promising alternative anti-corrosive material for the surface finishing layer of high-reliability devices.